WL#3121: Implement server and user editing for MySQL Explorer

This task involves implementing basic administration of servers and users inside
MySQL Explorer.

Much of the code involved in this is already written and will just need to be
moved over into this project.

Servers and users will be viewable in a tree like structure inside the MySQL
Explorer toolwindow.  Graphics/icons for servers and users will be provided by
the GUI team.

The administration functions that will be supported for servers are:
Add server, remove server, start server, stop server.

The administration functions that will be supported for users are:
Add user, remove user, edit user.