Proper implementation of CBLQueryRow.localSequence

* It now always has the correct value even if includeDocs wasn't true
* Removed CBLView.sequences property; it's now a no-op
Fixed an NSLock misuse warning triggered by -waitForDatabaseNamed:
CBLModel shouldn't reflexively reload itself during -saveAllModels
Increase code coverage of public API in unit tests

...In response to Tommie's code-coverage analysis.
Part of #94.