Implement caching for big map
Make that a four dimensional array to cover all color and projection combinations
Change 4th D to mapmode, not color, fix if statements

No need to store which color mode we are using, since the pixels get
assigned a new color anyway. Instead the fourth dimension can store
which mapmode we are in so that all three map types can be stored.
Even better, drop the 4th D entirely

All three map types use elevation data, so it only needs to be stored
once for each projection. Building the biome map first is problematic,
but it needs work anyway.
Fix the biome map, check for low- and hi-res alt data
A separate method might be a little more flexible

I made this method in the course of testing many things; in the end this
is basically the same as the last version.
Merge branch 'DM_Fork' of https://github.com/DMagic1/SCANsat_DM into DMagic1-DM_Fork

Conflicts:
	SCANmap.cs

caching support
added big map height caching!