AndroidContext will cause it to default to android storage engine

https://github.com/couchbase/couchbase-lite-android/issues/431
Default to DefaultSQLiteStorageEngineFactory return val

https://github.com/couchbase/couchbase-lite-android/issues/431
Refactor based on the deletion of the DefaultSQLiteStorageEngine class

* Both AndroidContext and LiteTestContext now return the AndroidSQLiteStorageEngineFactory.

* Delete com.couchbase.lite.storage.SQLiteStorageEngine as the file doesn't get used anymore.

* Update couchbase-lite-java-core submodule.
Merge branch 'feature/issue_431_storage_engine'

Conflicts:
	libraries/couchbase-lite-java-core
Update submodule