API: SetLastTouchedTrack(tr)

[me2beats]

we have GetLastTouchedTrack(), but we haven't r.SetLastTouchedTrack(). Of course we can use
Main_OnCommand(40914,0) -- Track: Set first selected track as last touched track
but in that case we have to do this:

1) save current track selection
2) select only tr
3) Main_OnCommand(40914,0)
4) restore saved track selection