Update CMakeLists.txt

This commit includes checking whether ../data directory (from build directory) and ../../stk-assets directory (from build directory) exists or not. If they don't exist, then it gives error message for the corresponding directory. I have included the code for this on line 320.
Update CMakeLists.txt
added achievement banana lover
added an achievement banana lover
merged code with upstream master
Now IA don't fire a cake if the kart is driving too slow. Also correct some comments.
Merge remote-tracking branch 'remotes/upstrem/master' into skiddingAI
Don't fire a cake if the target kart is driving too slow.
Fixing #1263 and little bit refactoring
re-adding -help
Merge remote-tracking branch 'remotes/upstrem/master' into skiddingAI
A kart is now considered as slow if he is slower than the current kart.
Merge remote-tracking branch 'remotes/upstrem/master' into skiddingAI
Do not write to 2 buffers outside of renderLights()
Bloom: Blit fbo instead of using a shader
Dont print glGetError result, prefer DEBUG_OUTPUT
Directly draw on default fbo if dyn lights are disabled
Update video settings dialog
Merge branch 'Issue_1263'
PointLight: Use a 1/(1 + d + k d^2) attenuation

This is not physically accurate, but a 1/d^2 attenuation makes light
extend too broad, and went too high if close from the source.