Allow configuring selected timeline & initial time from blueprint

[Wumpf]

Selected timeline seems pretty straight forward: It's another "porting job" from app state to blueprint!

Initial time cursor position is also important so it's easy to share an rrd/rbl that points at a given point in time.

Open question here if we want a special "on-open" timecursor location: If we don't do that every move of the time cursor is a blueprint edit and that's likely not what we want (we could be clever about it though and write to the blueprint store only on start/stop/pause/seek-plus-mouse-release, not on play)