Threading rewrite to remove use of unsupported cross platform threading update of...

Threading rewrite to remove use of unsupported cross platform threading update of the GUI.

When Viking is run on a real Windows system (i.e. not just under wine)
 that has been built via the new cross build mechanism, it will lock up whenever a window is moved.

Remove all use of gdk_threads_enter() / gdk_threads_leave() and always use the main thread to update the GUI.
Thus make extensive changes to ensure updates are directed through gdk_threads_add_idle() or gtk_idle_add()
 and protection to prevent use of data that has gone out of scope.

This should be more reliable.