Convert for loop linq expression
Extract palette reading code into PaletteReader class
Move Palette code from TAUtil to Mappy
Extract IO logic from MapModel and MapTile

Move the IO logic into a new static class, MapIO
Restructure TNT and SCT read/write code

Core TNT and SCT reading and writing code
no longer knows about UI side bitmaps.
Mappy is now responsible for conversion to and from raw data
to whatever format it wants to use.
Rearrange constants in TAUtil
Replace magic numbers with constants
Move tile caching code into its own class
Allow unused cached tiles to be garbage collected
Add FileName property to HpiReader
Extract some TDF methods into TDFConvert class
Rename grids namespace to collections and include quadtree
Rewrite TNT and SCT IO logic

Reduces TAUtil's coupling to GDI+ Bitmap
and increases the general modularity of IO.