Don’t set replication progress to 0/0 when stopping

Backported https://github.com/couchbase/couchbase-lite-ios/commit/c42a6612a3f215e7cb3d894f42fba42f0be4f625
Made CBLDatabase.lastSequenceNumber faster

Instead of doing SELECT MAX(sequence) FROM revs
it now does SELECT seq FROM sqlite_sequence WHERE name='revs'
The sqlite_sequence table is where sqlite stores the last generated
primary key for that table.
DB info response will not include data_size by default

Pass data_size=true to include size in bytes.
If db has a lot of attachments, it will iterate over all attchments
to get file size, which can take a while making db unresponsive.
In my case I rarely need db size, so this parameter isn't important
by default