2013collab: Initial optional collaboration client/server using zeromq

If the czmq and zeromq 3 headers are not available on your build machine this commit shouldn't do anything new.

If the ZeroMQ stuff is available then you'll have support for the new collaboration code! Select Collaborate/Start Session... to start a local collaboration server. The dialog will tell you where that is so that you can connect clients from other machines and platforms to the session. To connect to an existing session use Collaborate/Connect to Session. 

The server itself runs as a separate process, the $bindir/FontForgeInternal/fontforge-internal-collab-server process to be exact. Starting a server will launch that process for you. It can outlive the fontforge process and you can easily remove it by calling Collaborate/Close local server. Being a separate process, if you start a server and then have fontforge crash on you, then you can restart fontforge and connect to your own local server again (Connect to Session).

Most of the focus has been on selections and moving nodes in the charview. The metricsview undo doesn't seem to do anything right now, and didn't seem to do anything in fontforge-20120731-b.