* decouple image capturing from image post-processing and encoding
* post image-captured message after image is captured
* post preview-image message with snapshot of captured image
Default view finder sink in camerabin is autovideosink which doesn't
support xoverlay iface. If application decides to use another sink
that supports xoverlay, then it can use the interface directly.
Application developers won't know right away which module an interface comes from,
and may assume that it is covered by the usual GStreamer API guarantees, so make
it as clear as possible that this particular API is still subject to change
(should have done that with other libraries in -bad before too really).
