[SPARK-7830] [DOCS] [MLLIB] Adding logistic regression to the list of...

[SPARK-7830] [DOCS] [MLLIB] Adding logistic regression to the list of Multiclass Classification Supported Methods documentation

Added logistic regression to the list of Multiclass Classification Supported Methods in the MLlib Classification and Regression documentation, as it was missing.

Author: Mike Dusenberry <dusenberrymw@gmail.com>

Closes #6357 from dusenberrymw/Add_LR_To_List_Of_Multiclass_Classification_Methods and squashes the following commits:

7918650 [Mike Dusenberry] Updating broken link due to the "Binary Classification" section on the Linear Methods page being renamed to "Classification".
3005dc2 [Mike Dusenberry] Adding logistic regression to the list of Multiclass Classification Supported Methods in the MLlib Classification and Regression documentation, as it was missing.