[SPARK-7574] [ML] [DOC] User guide for OneVsRest

Including Iris Dataset (after shuffling and relabeling 3 -> 0 to confirm to 0 -> numClasses-1 labeling). Could not find an existing dataset in data/mllib for multiclass classification.

Author: Ram Sriharsha <rsriharsha@hw11853.local>

Closes #6296 from harsha2010/SPARK-7574 and squashes the following commits:

645427c [Ram Sriharsha] cleanup
46c41b1 [Ram Sriharsha] cleanup
2f76295 [Ram Sriharsha] Code Review Fixes
ebdf103 [Ram Sriharsha] Java Example
c026613 [Ram Sriharsha] Code Review fixes
4b7d1a6 [Ram Sriharsha] minor cleanup
13bed9c [Ram Sriharsha] add wikipedia link
bb9dbfa [Ram Sriharsha] Clean up naming
6f90db1 [Ram Sriharsha] [SPARK-7574][ml][doc] User guide for OneVsRest