[cleanup] removed _callback prefix from widget

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
[cleanup] removed trivial/rearely/internally used functions

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
[cleanup] removed trivial context functions

Context is an interface, all functions are pointers. The context
functions implemented in context.c were trivial wrappers.

The wrappers were removed, the function pointers can be accessed
directly.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
[hotfix] event queue modification while processing

 - event queue could be modified while being processed
 - queue was resized and pointer being accessed turned invalid
 - fixed by snatching the queue when processing
   -> new events are added to new queue
   -> old queue free'd after being processed

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
[fix] process remaining events after last window closes

 - When the last window closes, there may still be events in
   the internal queue
 - Continue processing events until queue is empty

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>