RoutePolar: Optimized Initialise() method

The IndexToAngle() function performed a division, a multiplication and
a substraction for every call in the for loop of the Initialise() method.
This could be reduced to one constexpr constant and one substraction for
each iteration.
i18n: Make a few string translatable

Fix #3520
Thread/CriticalSection: relicense to BSD 2-clause
po: update xcsoar.pot and *.po
Fonts: Deemphasise unimportant map labels

Draw map labels in dark gray, important map labels in black.
Don't use bold font.
DeviceListDialog: Render status line in small font
Fonts: Renamed FontHeight variable to font_height
Fonts: Don't draw map labels in italic

Italic is hard to read and the font size is indicator enough that these
labels are not waypoints, but topography.
Manual XCSoar-Handbuch: Move the current de wrap of the manual into a subdirectory, keep it as "Blitzeinstieg" and free the de directory for a 1:1 translation.
LX1600: Updated SetupNMEA() with information from the documentation

We have the official documentation now for these devices
LX1600: Added LXWP5 sentence to SetupNMEA() request string
LX1600: Added SaveToEEPROM() and FactoryReset() functions
Update doc/manual/de/Blitzeinstieg.tex

einfach nur eintest 
test: einfügen des winzigen bildchens.
test:  umgang mit git  und hochladen ..
manual.mk: Prepared manual build for a German translation,
added the path to the English version as last default to avoid copies for not jet translated file.
Manual: Reworked icons for config reference, gesture, and tip now in svg format.
Manual: Put new margin icons in xc manual style and deleted the replaced icon files.
Handbuch: nur ein TEst - keine wirkliche Änderungen
Manual: Warning sign in same style as other margin symbols.
manual: first collection of files for complete german manual XCSoar