Improve the mesh browser

[metallicafan212]

• Make it so meshes are organized into packages.
• Add material properties (like UE2) so the user can manually specify textures.
• Add in a animation track bar a la UE2
• Add in animation sequence properties (will probably have to be manual).
• Add in animation notify properties and the ability to add more (will have to manually do the properties).

[metallicafan212]

Made the browser organized by package rather than a gigantic list of all meshes.

[metallicafan212]

Greatly improved the mesh browser by allowing in editor imports, animation scrubbing, mesh properties, etc.

[metallicafan212]

All these have been added a while ago, I should really use this more often lol