Fixed broken SDL libraries linkage.

Add: CFLAGS and required SDL libs.
Change: Removed SDLmain linkage. Not needed.
Fixed game version info displayed in window title.
Fixed mixing of sound and music volume.

Music and Sound FMOD_SOUND entities are now grouped into FMOD_SOUNDGROUP
groups. When player would like to decrease the volume of sounds or music
we just decrease the volume of the responsible sound group.
Fixed sound volume and position interpolation.