Sound volume is now assigned in the GameRunner.

A warning is now printed if a stereo sound effect is loaded (i.e. not
positionable in 3d).
Added missing default sound effect. Added method for retrieving a sound effects duration.
Added warning message if the sound effect is too long. Added footstep sounds

Added functionality to see if a resource is of a specific type.
Added first step for music implementation
Added music integration
Used a better windows filesize function. It's now possible to play and stream music.

SoundEffect and Music are no longer of the type Scriptable.
Fixed memory leak.