The gstreamer documentation is not particularly amazing on whether or
not this is necessary, but it's clear that some gstreamer events will
not be delivered to their handlers without a running glib loop. This
runs one loop for all pipelines, which should be more than enough.
Disclaimer: This may conflict in demodesk/neko with the dragdrop
feature. Anyone backporting this bug fix to that repo should
investigate whether the loop created by `gtk_main()` will conflict with
this one before blindly porting.
Fixes#380Fixes#284