Extend CrossValidator with HasSeed in PySpark.

This PR replaces [https://github.com/apache/spark/pull/7997]

CC: yanboliang thunterdb mmenestret  Would one of you mind taking a look?  Thanks!

Author: Joseph K. Bradley <joseph@databricks.com>
Author: Martin MENESTRET <mmenestret@ippon.fr>

Closes #10268 from jkbradley/pyspark-cv-seed.

Added newlines before `:param ...:` and `:return:` markup. Without these, parameter lists aren't formatted correctly in the API docs. I.e:

![screen shot 2015-09-21 at 21 49 26](https://cloud.githubusercontent.com/assets/11915197/10004686/de3c41d4-60aa-11e5-9c50-a46dcb51243f.png)

.. looks like this once newline is added:

![screen shot 2015-09-21 at 21 50 14](https://cloud.githubusercontent.com/assets/11915197/10004706/f86bfb08-60aa-11e5-8524-ae4436713502.png)

Author: noelsmith <mail@noelsmith.com>

Closes #8851 from noel-smith/docstring-missing-newline-fix.

Author: Yu ISHIKAWA <yuu.ishikawa@gmail.com>

Closes #8694 from yu-iskw/SPARK-10284.

* Added isLargerBetter() method to Pyspark Evaluator to match the Scala version.
* JavaEvaluator delegates isLargerBetter() to underlying Scala object.
* Added check for isLargerBetter() in CrossValidator to determine whether to use argmin or argmax.
* Added test cases for where smaller is better (RMSE) and larger is better (R-Squared).

(This contribution is my original work and that I license the work to the project under Sparks' open source license)

Author: noelsmith <mail@noelsmith.com>

Closes #8399 from noel-smith/pyspark-rmse-xval-fix.

Author: MechCoder <manojkumarsivaraj334@gmail.com>

Closes #8110 from MechCoder/spark-9828.

The new test uses CV to compare `maxIter=0` and `maxIter=1`, and validate on the evaluation result. jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #6572 from mengxr/SPARK-7432 and squashes the following commits:

c236bb8 [Xiangrui Meng] fix flacky cv doctest

This PR makes pipeline stages in Python copyable and hence simplifies some implementations. It also includes the following changes:

1. Rename `paramMap` and `defaultParamMap` to `_paramMap` and `_defaultParamMap`, respectively.
2. Accept a list of param maps in `fit`.
3. Use parent uid and name to identify param.

jkbradley

Author: Xiangrui Meng <meng@databricks.com>
Author: Joseph K. Bradley <joseph@databricks.com>

Closes #6088 from mengxr/SPARK-7380 and squashes the following commits:

413c463 [Xiangrui Meng] remove unnecessary doc
4159f35 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into SPARK-7380
611c719 [Xiangrui Meng] fix python style
68862b8 [Xiangrui Meng] update _java_obj initialization
927ad19 [Xiangrui Meng] fix ml/tests.py
0138fc3 [Xiangrui Meng] update feature transformers and fix a bug in RegexTokenizer
9ca44fb [Xiangrui Meng] simplify Java wrappers and add tests
c7d84ef [Xiangrui Meng] update ml/tests.py to test copy params
7e0d27f [Xiangrui Meng] merge master
46840fb [Xiangrui Meng] update wrappers
b6db1ed [Xiangrui Meng] update all self.paramMap to self._paramMap
46cb6ed [Xiangrui Meng] merge master
a163413 [Xiangrui Meng] fix style
1042e80 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into SPARK-7380
9630eae [Xiangrui Meng] fix Identifiable._randomUID
13bd70a [Xiangrui Meng] update ml/tests.py
64a536c [Xiangrui Meng] use _fit/_transform/_evaluate to simplify the impl
02abf13 [Xiangrui Meng] Merge remote-tracking branch 'apache/master' into copyable-python
66ce18c [Joseph K. Bradley] some cleanups before sending to Xiangrui
7431272 [Joseph K. Bradley] Rebased with master

Fixes bug with PySpark cvModel not having UID
Also made small PySpark fixes: Evaluator should inherit from Params.  MockModel should inherit from Model.

CC: mengxr

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #5968 from jkbradley/pyspark-cv-uid and squashes the following commits:

57f13cd [Joseph K. Bradley] Made CrossValidatorModel call parent init in PySpark

Multiline commands are properly handled in this PR. oefirouz

![screen shot 2015-05-07 at 10 53 25 pm](https://cloud.githubusercontent.com/assets/829644/7531290/02ad2fd4-f50c-11e4-8c04-e58d1a61ad69.png)

Author: Xiangrui Meng <meng@databricks.com>

Closes #6001 from mengxr/SPARK-7474 and squashes the following commits:

b94b11d [Xiangrui Meng] update ParamGridBuilder doctest

Temporarily disable flaky doctest for CrossValidator. jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #5962 from mengxr/disable-pyspark-cv-test and squashes the following commits:

5db7e5b [Xiangrui Meng] disable cv doctest

Since CrossValidator is a meta algorithm, we copy the implementation in Python. jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #5926 from mengxr/SPARK-6940 and squashes the following commits:

6af181f [Xiangrui Meng] add TODOs
8285134 [Xiangrui Meng] update doc
060f7c3 [Xiangrui Meng] update doctest
acac727 [Xiangrui Meng] add keyword args
cdddecd [Xiangrui Meng] add CrossValidator in Python

as suggested by justinuang on #5601.

Author: Xiangrui Meng <meng@databricks.com>

Closes #5873 from mengxr/SPARK-7329 and squashes the following commits:

d08f9cf [Xiangrui Meng] simplify tests
b7a7b9b [Xiangrui Meng] simplify grid build

Author: Omede Firouz <ofirouz@palantir.com>
Author: Omede <omedefirouz@gmail.com>

Closes #5601 from oefirouz/paramgrid and squashes the following commits:

c9e2481 [Omede Firouz] Make test a doctest
9a8ce22 [Omede] Fix linter issues
8b8a6d2 [Omede Firouz] [SPARK-7022][PySpark][ML] Add ML.Tuning.ParamGridBuilder to PySpark