MacGui: Initial implementation of drag and drop in the presets drawer.

MacGui: Initial implementation of drag and drop in the presets drawer.
- Allows drag and drop arrangement of custom user presets
- Does not allow reordering of built in presets.
- Sorting of presets now done only by type ie. built in and custom user.
- Provides functionality for future nested presets and drag and drop arranging.
- Subclasses the presets outline view for better control over drag and drop behavior

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@1334 b64f7644-9d1e-0410-96f1-a4d463321fa5