Also removes the TILES_AT_COMPILETIME cmake option.
Previously tilecreator was compiled by cmake and then executed
to generate tiles from srtm.jpg. The size difference between both
is not large (3.1 MB vs 3.8 MB) so the additional complexity is
avoided now and the generated tiles are placed in data/ directly.

This does not affect the installation result in any way. Just the
source repository grows slightly.

tilecreator is now available from tools/tilecreator/ and can be
compiled using cmake.