Core features for Timeline class

Basic playthrough, pause, loop, animation and global frames.
Unit tests to support this.
Add support for playing backwards

Add the ability to play the timeline forward or backward. This is
supported via the direction property.
Throw custom error if trying to advance without an animation set
Use only animation data for Timeline

Previously the Timeline class was using the whole data manifest model,
change it so that it only works with the "animations" subset of the
manifest.
Merge branch 'feature/timeline' into develop