rtsptransport: add GType for Profile

See https://bugzilla.gnome.org/show_bug.cgi?id=720696
rtsptransport: add method to get media-type from transport

Add a method to make a media-type from the transport. Deprecate the old
method that only used the mode.

Based on patch from Aleix Conchillo Flaqué <aleix@oblong.com>

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=720219
rtsptransport: calculate default lower transport

Add an internal method to calculate the default lower transport whan it
is missing.
defs: update for new symbols
tests: videodecoder: add simple playback test

Add a simple playback test that makes sure that video decoder pushes
buffers in the same order it receives and that it respects the
set timestamps and durations
tests: videodecoder: add check for serialization of events

Tests that events are properly serialized with buffers, also checks
that the usual events are sent (stream start, caps, segment and eos).
riff: Add G726 ADPCM support

https://bugzilla.gnome.org/show_bug.cgi?id=720995
videoconvert: remove unused code
videoconvert: fix I420 to BGRA fast-path some more

Calculate alpha value differently so that we can avoid running out
of registers.
videoconvert: rework YUV->RGB fastpaths

Rework the orc code to be around 10% faster and support arbitrary matrices.
Pass the matrix parameters to the YUV->RGB functions to make them work
for all matrices. This enables more and faster fastpath conversions.

See https://bugzilla.gnome.org/show_bug.cgi?id=721701