AirspaceLook: move attributes to struct AirspaceClassLook
AirspaceRenderer: add local reference variables

Simplify the code.
AirspaceClassLook: add attribute fill_color

Copy from AirspaceClassRendererSettings::fill_color.  Prepares for
using the "portable" Color classes in AirspaceClassRendererSettings.
Screen/PortableColor: add methods Darken(), Lighten()
Screen/PortableColor: add RGB8Color::operator==()
Screen/PortableColor: add color constants
Screen/Color: add conversion constructor from RGB8Color
AirspaceRendererSettings, Formatter/HexColor: use RGB8Color

Use the portable color class for profile settings, which is important
because some non-portable Color implementations may be lossy (e.g. 16
bit RGB565).
Screen/Ramp: return RGB8Color
SDL/Canvas: move code from map() to Color::Map()
Screen/PortableColor: fix return type of GetLuminosity()
Screen/PortableColor: move code to FromRGB()
Screen/PortableColor: add Luminosity8 constructor from RGB8Color
Screen/SDL: add option "GREYSCALE"

To be used by the KOBO port.  This is currently extremely slow because
SDL_gfx and SDL are very bad at 8 bit rendering: they assume it's a
surface with a palette, and waste an enormous amount of CPU cycles in
palette lookups.  This will be optimised later.
SDL/Color: remove duplicate constructor

Remaining garbage from a merge conflict.
DebugReplay: split CreateDebugReplay to allow calling with file name instead of args.
DebugReplay: move NLineReader out of DebugReader class

Prepare creating a DebugReplay from a std::vector.
skylines: tool to read igc file to std::vector

This is intended for a future python api to xcsoar. Therefore the
simple FlightFix struct which will be used to share a igc file
between xcsoar and python.
FlightFix: add availability flags
DebugReplayVector: replay from std::vector