Adding support for @Index.
Merge branch 'master' of github.com:realm/realm-java into kg-index-annotation

Conflicts:
	changelog.txt
	realm-annotations-processor/src/main/java/io/realm/processor/RealmProcessor.java
Update changelog.txt
Merge branch 'master' of github.com:realm/realm-java into kg-index-annotation
Feedback from PR review.
Merge branch 'kg-index-annotation' of github.com:realm/realm-java into kg-index-annotation
Merge pull request #458 from realm/kg-index-annotation

Index annotation