Remove flickering on resize and get rid of the aspect frame

[Filippo Argiolas <fargiolas gnome org>]

The "noflicker" branch implements a couple of things I wanted to get
in since some time.
- remove GtkAspectFrame and let gstreamer do the  keep-aspect-ratio work.
This adds black bars to the image giving it a nicer look IMHO and
making it more consistent with the other video applications (e.g.
totem and empathy).
- remove padding between the video and the window border (bug 559188)
(caused by the aspectframe)
- remove that ugly flickering (gtk+ competes with the overlay in
drawing the drawing area background) that happens on window resize

The black bar thing is not a trivial change in the overall look so,
please, test it and tell me your thoughts.

ciao,
Filippo