Fixed ReplicationTest 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.
Fixed ReplicationTest 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.
Fixed TestHeaders. Fixed TestGoOffline.

Also working on TestGetRevisions, which only fails when
running all tests. When running all ReplicationTests,
or by itself, it passes just fine. Fails to Stop
quickly enough when it does fail.
Merge pull request #16 from xamarin/replication-test

Fixed ReplicationTest's failed tests