Added -installCannedDatabase:withAttachments: method

Allows you to ship a database file with an app and then install it on
the first launch.
Added API for creating persistent replication even if one already exists

This allows for multiple replications with different filters, between
the same databases.
Added -[CouchDocument refresh] for use with remote servers without tracksChanges

It will validate the cached currentRevision, if any, against the server and update it if it changed.