Add sound effect for call joined / left (#2794)

* Add renderer for call joined / left

* lint

* Add new sounds

* Updates sounds in renderer

* lint

* move import

* pad sounds with silence

* lint

* tidy

* Drop autoplay since we now subscribe correctly.

* Comitting test files I am going to be going to lunch so will tidy up in a little while.

* finish up tests

* Add support for multiple channels per sound.

* lint

src/sound/LICENCE.md

@@ -19,4 +19,6 @@ The following sound effects have been originally created by Element.
 - `end_talk`
 - `start_talk_local`
 - `start_talk_remote`
+- `join_call`
+- `end_call`
 - `reactions/rock`