[SPARK-14472][PYSPARK][ML] Cleanup ML JavaWrapper and related class hierarchy

Currently, JavaWrapper is only a wrapper class for pipeline classes that have Params and JavaCallable is a separate mixin that provides methods to make Java calls.  This change simplifies the class structure and to define the Java wrapper in a plain base class along with methods to make Java calls.  Also, renames Java wrapper classes to better reflect their purpose.

Ran existing Python ml tests and generated documentation to test this change.

Author: Bryan Cutler <cutlerb@gmail.com>

Closes #12304 from BryanCutler/pyspark-cleanup-JavaWrapper-SPARK-14472.