V6 zoom map fix

It probably warrants a bit more testing, but it seems ok when I tried it.

I added a small, second cache to be used by the zoom map, that seemed easier than trying to avoid using the cache at all for the zoom map. 

The changes in SCANui are mainly to the resetMap calls. An extra parameter was added to the SCANmap.resetMap method, this determines which height map array is to be used. 

The changes in SCANmap reflect this added parameter. I also added a reference to that parameter in all of the calls to the heightMapArray() method, so that the correct array is written to.  Thankfully the zoom map and the big map use different methods to set the actual map size (setSize() and setWidth(), respectively) which simplifies things.

The only functional change for the end user is that they can't open a zoom map while the main map is still re-building. They have to wait until it is complete (they can re-build the bigmap while the zoom map is rebuilding though, not sure why that doesn't break it too) before right-clicking does anything.