add option to include conflicts in ChangeTracker constructor

This design was chosen because it matches iOS' CBLChangeTracker class.
The includeConflicts option makes the change tracker request the remote
changes feed with the "style=all_docs" option, which is required for
replication.
Fix for issue #77.  Fixed via the same approach as used in Couchbase Lite iOS.

https://github.com/couchbase/couchbase-lite-java-core/issues/77