MSVC and CMake fixes

 * libfalltergeist now compiles automatically!
 * add ability to force external libfalltergeist
 * add missing headers
 * add MSVC implementation of dirent.h
 * add MSVC implementation of clock_gettime()
 * fix MSVC C2797 http://msdn.microsoft.com/en-us/library/dn793970.aspx
 * fix SDL library finding for MSVC

NOT Ready for merge!

There is error with EventHandler:
```
\src\Game\GameObject.cpp:181:1
error C2440: 'type cast': cannot convert from 'void (__thiscall Falltergeist::LocationState::* )(Falltergeist::MouseEvent *)' to 'Falltergeist::EventRecieverMethod'
```

so, all lines with```->addEventHandler``` contain this error


Also, only MSVS 14 CTP is compatible with falltergeist (because of unrestricted unions feature)
http://www.visualstudio.com/en-us/downloads/visual-studio-14-ctp-vs.aspx