Port Futon2 local replication target work to Futon

Futon2 currently has a patch that makes the replication target into a text input, using jQuery UI's autocomplete widget to still provide the "all databases" functionality. If the database doesn't exist, then the user is prompted to see if they want it created with a JS confirm() prompt. If they do, then the create_target replication option is set to true.

This will be a port of this Futon2 pull request: https://github.com/BigBlueHat/couchdb/pull/1