Resolve workspace rename issues (RM7883)

Resolves RM7883:
https://dev.metasploit.com/redmine/issues/7883

by re-creating the default workspace when it is being renamed.

Also resolves an issue when renaming the active workspace and then listing workspaces. The error was independently verified by bonsaiviking:
http://pastebin.com/HMw92Xxk

and is resolved by switching to the new workspace name if the old workspace is active.