QT Plugins

Here is an interesting link which I believe pertains directly to us. I
ran into this problem because we have certain function that we will want
to expose to the plugins. Most notably we will want a lot of GL
functions to be exposed to the plugins. Because of this I believe it
would be good to extract our GLEngine to a library. We had talked about
doing this later so that it could be used by other apps but it seems
like to move on it would be good to do this now. I’m going to commit
the code. It works from xterms (and i’m not sure if it’ll work for you
in Mac but I am adding some of the QT suggested code for loading plugins
on OSX). Going to commit what i have so far then work on separating out
the GLWidget and Engines to libavogadro.