situation_at_point: 160 deg .. 200 deg is also counted as "back"

As a test case, the situation at Hohenstaufenstr./Muenchener Str. is
used.
SRTShortcuts: better situation_at_point plotting

* text layer is now topmost
* using outline_text instead of normal Canvas createText
SRTShortcuts::show_situation_at_point_for_route: update cgi heuristics

The function now implements also the cgi heurstics for "turn back".
data update (minor)