References #2314: Added access restriction modifiers to AbstractTransformer to restrict what becomes API.  Added documentation.

Change-Id: I764e986addee7ccff666a8e8889ffa0a921df705
Merge branch 'develop' into release/3.1.0
Refs #2320: Adds displayName property to DataCategory.
References #2315: Added Javadoc for filter-api

Change-Id: I3afd70ea18da2f98cc17e9f68f7148856e22c51e
Refs #2359: Deprecates vizmap-gui-api interfaces and methods that don’t make sense in version 3.1.
Merge branch 'release/3.1.0' into develop