Add AtlasWriteClient interface for writiing people to an Atlas

Add interface for writing with a writePerson method, implemented by
GsonAtlasClient.
Merge branch 'mbst-6741-post-people' into stage

* mbst-6741-post-people:
  Add AtlasWriteClient interface for writiing people to an Atlas

Conflicts:
	src/main/java/org/atlasapi/client/GsonAtlasClient.java
	src/main/java/org/atlasapi/client/GsonQueryClient.java