rtpsession: Don't try to return srtpenc/dec if not installed

https://bugs.freedesktop.org/show_bug.cgi?id=85566
rtp-discover-codecs: Make global access to blueprints thread-safe

The global variable list_codec_blueprintfs refcounted with codecs_list_ref
was not thread safe. This patch uses a global lock to make this code path
thread safe.

https://bugs.freedesktop.org/show_bug.cgi?id=85567
Fix clang warnings

https://bugs.freedesktop.org/show_bug.cgi?id=85565
nicestreamtransmitter: expose port range setting from libnice
Add ICE-TCP candidates

Also to the nice transmitter
nice: Add support for reliable nice agent and selection of ice-udp/ice-tcp
rtpsession: Add support for send-rtcp-mux on fs-rtp-session and nice transmitter
fs-gui: Remove duplicated FsUIParticipant
fs-gui: Remove implicit __del__() with explicit destroy() calls
nice-transmitter: Fix off-by-one

In fs_nice_transmitter_set_send_component_mux(), the component IDs,
which start from 1, are used as nicesinks array indexes and
nicesinks[0] is always NULL.
Revert "nice stream transmitter: Ignore ICE-TCP candidates for now"

This reverts commit 137e5607083f1b7522849c3e1f5976736ca0d098.
Revert "Requirement is actually 1.4 for srtp"

This reverts commit baf132613b41ff2f7acaf54abe6cd2111046d43b.