Implement TagDataRepository. Fixes T1081

Summary:
 - Add tag entity class
 - Add tag entity mapper class
 - Add tag database helper class
 - Add Tag data repository class
 - Add TagEntity test
 - Update data module to use java 7 for building otherwise it breaks build.
 - Add TagEntityMapper test
 - Add tag database helper tests
 - Add test case for tag data repository

Test Plan:
Run
 - ./gradlew test

Reviewers: dalezak, PapaLee, shadowhand

Reviewed By: shadowhand

Subscribers: dkobia, rjmackay, shadowhand

Maniphest Tasks: T1081

Differential Revision: https://phabricator.ushahidi.com/D505