Don't send inbound session to self and claim and send all keys at once.

Also fixes some resize issues with stupid workarounds to our resize
logic. This really needs to be cleaned up at some point!

Integrating that in our CI is currently a bit hard, so disable it for
now, if GStreamer isn't found. Just make sure to build against GStreamer
for call support!

While it does improve performance a bit, it is simply bad for most
distributions, since they don't know and probably don't want to
recompile Nheko. So default it to off. Anyone who wants it can still
toggle it on and it is almost no maintenance cost.