Math/Angle: don't use optimised multiplication for Angle*fixed

Reverts the second part of e4b9b576.  Turns out that the
CatmullRomInterpolator does care a lot about the bits discarded by the
fast_mult() call, because it passes very small values (TRAC #2537).
The unfortunate bottom line is we can't predict the dynamics of the
two factors, and we must not discard any bit in the default operator
without knowing from where this was called.
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
Form/DataField/Angle: Add option to enable fine adjustment of values
Dialogs/Task/SectorZoneEditWidget: Enable fine adjustments of radials

Implements trac request #2540.
Form/DataField/Angle: Fix rounding issues on angles.

Due to rounding issues a 360° was sometimes present in
the ComboBox leading to an assertion on selection.
Prevent this issue by enforcing the range 0 - 359 for values.
build/android: Added ICON_PNG variable to merge duplicate code
build/android: Generate icon from SVG directly
build/android: Build icons for all common resolutions
LX1600: Fixed API documentation