(This commit also modifies UI)
Instead of pinging Twitch every time the program starts up, only pings
for new servers when the ingests are actually being used, and when the
UI uses the auto-configuration dialog.
If ingests have not been cached when using the "Auto" server, it will
wait for 3 seconds max to query the Twitch ingest API. If it takes
longer than 3 seconds or fails, it will defer to SF. If ingests were
already cached, then it will use the existing cache immediately.
d768717b8c