Visualization: improved Rstc code and animation.

Got rid of a few ugly variables (t0, tStartOffset, tSitOffset).
Added: Rstc has start argument to set initial starting time.
Added: Rstc.start() which returns time of since offset.
Modified: Rstc.wait(t) is now more efficient when called directly after
          another Rstc.wait(t), so that Rstc.wait(t) can be used instead
          of Rstc.time(t) to advance time further.
Removed: Rstc.time(t) as modificator of time.