Merge pull request #101 from matthewrice345/master

DiscussionTopicHeader update
Add GroupCategory, Group methods

Add methods to create and delete groups, get people from
groups, and creating group categories.
Update GroupCategoriesAPI to follow style guidelines.
Merge pull request #102 from bradylarson/master

Add GroupCategory, Group methods
Updated gradle file for Android Studio 1.0 Stable Release and Gradle 1.0