[SPARK-15243][ML][SQL][PYTHON] Add missing support for unicode in Param methods & functions in dataframe

## What changes were proposed in this pull request?

This PR proposes to support unicodes in Param methods in ML, other missed functions in DataFrame.

For example, this causes a `ValueError` in Python 2.x when param is a unicode string:

```python
>>> from pyspark.ml.classification import LogisticRegression
>>> lr = LogisticRegression()
>>> lr.hasParam("threshold")
True
>>> lr.hasParam(u"threshold")
Traceback (most recent call last):
 ...
    raise TypeError("hasParam(): paramName must be a string")
TypeError: hasParam(): paramName must be a string
```

This PR is based on https://github.com/apache/spark/pull/13036

## How was this patch tested?

Unit tests in `python/pyspark/ml/tests.py` and `python/pyspark/sql/tests.py`.

Author: hyukjinkwon <gurwls223@gmail.com>
Author: sethah <seth.hendrickson16@gmail.com>

Closes #17096 from HyukjinKwon/SPARK-15243.