Tweak some graphics
Merge branch 'master' of https://github.com/nczempin/Turris-Monacoae
Add "toon effect", when shadows are deactivated.
different towers can now be selected for building

with the keys 1 - 4. After that, a mouse click will build the tower.
Note: The value 2 is skipped because it would let the player build the
main base right now.
Merge branch 'master' into nczempin