Synchronized playback of multiple replays

[ThagonDuarte]

When testing #1253 it was found to be tedious to manually sync up two different running replayers. It would be way more convenient to have one UI with one timeline, which controls multiple replayers.
One possible way of doing this is introducing another layer above a single replayer. The unified timeline client would communicate with each running replayer and set their current time frame, start playback, set playback speed etc.
This would essentially only strip the existing replayer of its UI, which is moved to the unified client, but keep all the core functionality of actually playing back a replay.

When this is couples with #1541, multiple instances of twiy could then display these different but synced up replays simultaneously.

An even better, but way more intense and tike costly, change/rewrite could also be to move twix from a single robot model to a multiple robot model, where all replays would be able to be displayed in a single twix instance.