SnailTrail: precalculate color of each point, and no more need to store the vario float.
We gain both drawing speed and some memory.
Removed unused SKIPPOINT code and added DEBUG mode .
	modified:   ../Header/MapWindow.h
	modified:   Calc/AddSnailPoint.cpp
	modified:   Draw/LKDrawTrail.cpp
SnailTrail: skip empty points in the array.
More distance between points painted by LKDrawTrail . Using the Manhattan distance formula this is only a very approximated attempt.
Previously using 2 pixels at high zoom, and 4 at low zoom, resulting in too many points painted with no reason.
These are now raised to 8 and 14 , generally valid for all resolutions.
We must avoid the "snake effect" of a color-chaning trail!
	modified:   Draw/LKDrawTrail.cpp