Allow stopping an active race

[Henrik Heimbuerger]

This probably just requires a toolbar button in the race perspective that tells the RaceEngine to stop and switches back to the design perspective.

[SVN]

New commit by frohn (revision [214]):
[Fix for ticket #64, partial fix for ticket #42] Stop Race Action stitches back to initial perspective

Furthermore I redesigned the actionsets for a better handling between the different perspectives.

[SVN]

New commit by frohn (revision [229]):
[Fix for ticket #14 and #64] Start- and StopRaceAction? inherit from union parent (abstract class RaceControl?)

This solution has the effect that both action get the same RaceEngine? and the code is well arranged and minimized.