Improve bitmap importing for Halo 1

[GoomiiV2]

Atm the bitmap importing is simple, it just get all the bitmap tags and extracts the bitmap plates and creates texture assets in Unity.

I'd like to improve this to go off the shader tags and create a rough version of that shader in unity, as in shaders with transparency will also have transparency in Rampancy.
And to also only import texture that are used in levels, atm it imports all bitmap including those for the ui and models.