support effects

[Luis de Bethencourt Guimerá]

filter the videos through one effect. right now gstreamer has some effectv bassed effects, but it would be nice to work in having freeframe filters in gstreamer.

to implement having a passtrough element and then changing dynamically this one in a running gst pipeline...

read:
http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-block.txt

(section...)
* dynamically switching an element in a PLAYING pipeline.

  .----------. .----------. .----------.
  | element1 | | element2 | | element3 |
 ... src -> sink src -> sink ...
  '----------' '----------' '----------'
                    .----------.
                    | element4 |
                   sink src
                    '----------'