This is a prefered method to allow limited access to the TURN server

this fills out the infos in /_matrix/client/r0/voip/turnServer with
values specified in the server config

Remove device_one_time_keys_count from is_empty() sync checks, fixing sync issue as reported by Nekron

Should make the code a little bit easier to read.

Co-authored-by: Timo Kösters <timo@koesters.xyz>

We now ask the trusted server for all keys in 1 request, instead of
asking each server individual for it's own keys.

to device events were not being sent