Moved tests -> unittests

unittests/test_chat_session.h

@@ -0,0 +1,4 @@
+void returns_false_when_chat_session_does_not_exist(void **state);
+void creates_chat_session_on_recipient_activity(void **state);
+void replaces_chat_session_on_recipient_activity_with_different_resource(void **state);
+void removes_chat_session(void **state);