don't wait for codec initialization to accept connections

[totaam]

Following up #2341, we now wait for the init thread to complete (r21937). See also #2415 and #2411
We could try to accept the client connections first and later update the client with the new list of codecs.

[totaam]

Done:

• r24311 (+r24313 fixup) + r24314: we only wait for connections that need access to the encodings
• r24315 (+r24316 fixup) new encodings.packet capability
• r24317 (+r24318 fixup) html5 client support
• r24319 remove test code

Warning: the code to update the tray menu is a bit iffy, we monkey patch the packet handler to update the tray menu when the encoding attributes are received.

[totaam]

Ensure we can use 'png' and 'jpeg' early, even before the threaded initialization has completed: r24341.