aacparse: fix object_type parsing off-by-one in ADTS frame

According to http://wiki.multimedia.cx/index.php?title=ADTS,
the value stored in ADTS headers is one less than the object
type of the AAC stream.

A look at ffmpeg shows it also adds 1 to the value read off
the ADTS header.

Note that this might break other things that happen to have
an inverse off by one to match the existing code.
aacparse: allow conversion from ADTS to raw AAC

Some muxers (eg, qtmux) only support raw AAC, so this allows linking
an encoder that outputs ADTS only to those muxers.

The conversion is simple (omit the first 7 or 9 bytes of the frame),
but has to be done in pre_push instead of handle_frame as 1.0 does
not seem to allow skipping bytes there as 0.10 used to.

Other conversions are not supported (yet).
jitterbuffer: add some more debug
session: remove source from sync_rtcp

We don't need to know the sender source of the session in the
callback, the SR packet is for all participants in the session.
session: refactor add and find source

Make functions to find and add a source to the hashtable.
session: configure sdes with structure only

Remove code to configure the SDES with methods and types, only
allow configuration with GstStructure
source: also use the source for bye_reason

Store the BYE reason in our internal source object. Rename the methods on the
source object a little because now the BYE can be received in RTCP or
set when the session wants to send BYE.
source: reset more
session: let source keep track if it sent BYE
session: do nicer checks for internal sources
session: parse packet outside of the session lock
session: move check for is_early around

Move the check for the early RTCP to where it is needed and used.
session: Rearrange RTCP reporting a little

Make a function to generate an RTCP packet for a source, pass the source as a
parameter.
Move timeout of collisions to session cleanup phase.
session: add some docs
session: fix bandwidth calculation

We iterate over all sources and the internal one is also in the
hashtable so avoid adding it twice.
session: get SSRC from RTCP packet itself

Get the SSRC from the RTCP packet instead.
rtpsession: separate BYE marking and scheduling

First mark sources with BYE and then schedule the BYE RTCP message.
session: count internal sources and how many are senders
session: make method to make internal sources

Add a method to obtain an internal source and use it to create
our internal source
session: keep SDES and set on new internal sources

Keep track of the SDES ourselves and set it on all newly created
internal sources.