Some initial changes to filter incoming docs by id

Get some test cases passing

Use batcher to pull in missing revisions at the beginning of replication

Move most of the filtering into TDPuller where it properly belongs

doSetClientFilterDocIds -> setClientFilterDocIds

Address PR feedback:

* Add more comments/documentation
* Smarter way of fetching document filter sets
  (use getDocWithIDs instead of getAllDocs)
* Add more tests

Add example usage to clientFilterDocIds

Fix client filter algorithm:

* Pull all missing documents first (those that are in the filter list
  but not in the database), without updating sequence number

* Update all documents currently in database, updating sequence number

Immediately insert new downloads when filtering by ID

Pull document ID fixes:

* Implement PR feedback
* Remove unused variables and fix comments

Fix compile error

Add assert on seq no

Remove unused variable 'count'

Implement some PR feedback