Fixed ReplicationTest's failed tests

- Run and fixed tests in ReplicationTest
- Ported Get/Set Channels from Android
- Implemented an intermediate solutions for stopRemoteRequests() in Replication.cs
- Fixed bugs in Replication.UpdateProgress() when setting LastError
- Fixed bugs in Replication.UpdateProgress() when initializing remoteLastSequence
- Fixed bugs in Replication.Is404 by correcting the type check
- TestHeaders is still failed.