DigitEntry: Assure that entry form fits into available screen width

Fixes trac issue #3069.
src/MapWindow/GlueMapWindowDisplayMode.cpp, src/Look/MapLook.?pp, src/Renderer/CompassRenderer.cpp, manual: Improvement of North arrow

The goals of this commit are
1/ to improve the graphical layout of the North arrow, now like conventionnal North arrow. now clearly different from other arrows used on map
2/ to improve its display logic. It now simply displays the North arrow as soon as circling or cruise is set to a different orientation than North up. The logic will not change current behavior for users chosing North up for both circling and cruise orientations (no North arrow).
CompassRenderer.cpp: Improvement of North arrow

This commit adds black on right half of the North arrow, and displays the North arrow only if either cruise or circling orientation is not set to North up.
src/MapWindow/GlueMapWindowDisplayMode.cpp: replace 0/1 by false/true