Linux Support for Game

Here are some Linux support patches. I've been able to compile the three targets and to play the entire Case without problem but code is still missing in launcher and updater to use them.

- Added CMake build
- Updated CobeBlocks project by mbasaglia (untested since I don't use it)
- Load Cases
- Load / Save game
- Set Common Data directory to "/usr/share/MyLittleInvestigations" by default, can be changed when configuring the build (-DCOMMON_DATA_DIR=... on the cmake cmd line, also setup in the game CodeBlocks project)
- Set per user directory to "~/.local/share/EquestrianDreamers/MyLittleInvestigations" (path resolved by SDL).

Thanks to mbasaglia since he did most of the linux specific implementation.