Dynamically build menu-items based on configured proxies

In case you're interested, I've refactored the code to only show menu-items for proxies which are configured (whether or not they are actually enabled) and added support for FTP and RTSP proxies.  And, since there are now 5 proxies this will support, reverted back to the 2-state menu-icon rather than create a 32-state version =/