rtpgstpay: pre-allocate buffer list of the right size

To avoid re-allocs.
rtpvp8pay: couple of minor optimisations

Pre-allocate buffer list of the right size to avoid re-allocs.
Avoid plenty of double runtime cast checks and re-doing the
same calculation over and over again in rtp_vp8_calc_payload_len().
Only call gst_buffer_get_size() once.
rtpvp8pay: post error message on bus on error and don't use g_message()
rtpvp8pay: allocate bitreader on the stack
rtpmp4vpay: pre-allocate buffer list of the right size
rtpjpegpay: pre-allocate buffer list of the right size
rtpjp2kpay: pre-allocate buffer-list of the right size
avidemux: don't leak flow combiner
rtpjpegpay: propagate the GST_BUFFER_FLAG_DISCONT flag

Propagate the DISCONT flag to the first RTP packet being used to transfer
a DISCONT buffer.

https://bugzilla.gnome.org/show_bug.cgi?id=730563
gstrtpmp4gpay: propagate the GST_BUFFER_FLAG_DISCONT flag

Propagate the DISCONT flag to the first RTP packet being used to transfer
a DISCONT buffer.

https://bugzilla.gnome.org/show_bug.cgi?id=730563
rtph264pay: propagate the GST_BUFFER_FLAG_DELTA_UNIT flag

Downstream elements may be interested knowing if a RTP packet is the start
of a key frame (to implement a RTP extension as defined in the
ONVIF Streaming Spec for example).

We do this by checking the GST_BUFFER_FLAG_DELTA_UNIT flag we receive from
upstream and propagate it to the *first* RTP packet outputted to transfer this
buffer.

https://bugzilla.gnome.org/show_bug.cgi?id=730563
rtph264pay: propagate the GST_BUFFER_FLAG_DISCONT flag

Similarly to what we did with the DELTA_UNIT flag, this patch
propagates the DISCONT flag to the first RTP packet being used to transfer a
DISCONT buffer.

https://bugzilla.gnome.org/show_bug.cgi?id=730563
vp8depay: fix header size checking

Use a different variable name to make it clear that we are calculating
the header size.
Correctly check that we have enough bytes to read the header bits. We
were checking if there were 5 bytes available in the header while we
only needed 3, causing the packet to be discarded as too small.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=723595
rtspsrc: add support for key length parameters

This patch adds supports for the incoming key management parameters for
encryption and authentication key lengths.

It also adds a new signal request-rtcp-key that allows the user to
provide the crypto parameters and key for the RTCP stream.

https://bugzilla.gnome.org/show_bug.cgi?id=730473
rtspsrc: pass the stream id when asking for crypto params

This way the app can choose different parameters for each stream.
multiudpsink: avoid some unnecessary run-time type checks
multiudpsink: optimisation: avoid unnecessary memory ref/unrefs

We know the buffer will stay valid and we will also not
modify the buffer, we just want to send out the data.
pulse, v4l2: update for device "klass" -> "device-class" rename
po: Update translations
Update .po files