add failing test for DocumentChange.isExternal() flag
mark DocumentChanges from remote sources as external

Makes ChangesTest.testPulledChangesAreExternal() pass.
Merge pull request #71 from mjq/is_external

Mark DocumentChanges from remote sources as external
Delete CouchbaseLiteApplication, not needed.
apparently gradle updated itself, or something in Android Studio did.
add testAttachmentDisappearsAfterSave() to try to reproduce issue #70.  unable to reproduce.

https://github.com/couchbase/couchbase-lite-android-core/issues/70
refactor a few android specific classes into their own package.