Native GeoTIFF Support

[weigert]

Changes:

• Introduced soillib/io/geotif.hpp
  • Native GeoTIFF support without GDAL (libtiff only)
• Separated tool from model, so that it is clear what each program is for.
• Made the tool utility programs a little bit more standardized, adding help strings
• Updated the viewer so it can handle GeoTIFF single files and directories at the same time.