MPEG4 Cleanup

[benrr101]

A buttload of cleanup changes to the MPEG4 implementation. Here's some highlights:

• Pretty much rewrote the AppleTag/ILST implementation
• Broke the circular dependencies in the MpegBox inheritance tree by implementing a separate renderer and moving the loadChildren implementation.
• public fields -> properties
• style changes
• added guards where necessary
• added tests for AppleTag