Added initial main thread invoker class.
Moved creation of OpenGLServerGrabber into HTTPServer, since this
manages its lifetime.
Added mainthread Invoker instance to HTTPServer, and use this in server
thread to fetch renderlist updates.
Added code that use mainthread invoker to transfer control when grabbing
images.
Removed redundant invoke-in-main-thread code in opengl-grabber.
Merge pull request #108 from sintefmath/cdyk_qt_run_functor_as_gui

introduces an invoker object in the HTTP server that handles running functions as the main thread. This is used for grabbing images from opengl and for creating renderlists.