Redo entire UI design using VGUI2

[SaintWish]

We should come up with a design that doesn't use too much textures and make the game more user friendly, especially the inventory system. If we use VGUI2 which is what the source engine uses I think it would allow us to do more with the UI.

[Tsarenir]

It would be fantastic to eventually have support for mouse-over tooltips, primarily thinking it'd be useful for items in the inventory to explain less user friendly features like level requirements and armor strength requirements, but I'm sure mapping could find uses as well.