The TTF font used by the navigation app is ~20KB and is stored in internal flash memory.
To free this space, the TTF font is now converted in 2 "atlas pictures" (pictures that contain multiple concatenated images) stored in the external flash memory. The navigation app now accesses one of those 2 files and apply an offset to display the desired picture.
The corresponding documentation has also been updated.
Add comments about the layout of the pictures that contain the icon and about the indexing of those icons.
In documentation (buildAndProgram.md), edit the section about the debug compilation mode. Remove the part about removing the Navigation app to free some memory (since it's not relevant anymore) and explain how to selectively build parts of the firmware in Debug mode.
Also, removed feature existance cheking (since it now depends on a font,
so may end up being inside (only) a font not being used currently -
which is an allowed usage)
