Fixed Issue #11: Generate 8 levels of super tiles by default.

During testing it turned out that the viewer requested levels 1-8.  It's better to build the default range by default!
Fixed Isue #12: Does not create tile folders if missing!

Program was crashing if the newtiles or mapttiles folder were missing.  Not sure how I missed this, but I am sure it wasn't a problem at one point!