Many changes supporting the pymclevel update.

Default values for regions were corrected, additional options for
dataset suffixes were added, optimizations were added to file
extraction.

Warped GeoTIFFs were never necessary after all, so they were removed
resulting in an improvement in performance.

First pass on setting the biome, with a "setBiomeAt()" added to the
tiles code until it gets added to pymclevel proper.

While fixing changes in items (Rose is dead, long live Poppy), a minor
annoyance in materialNamed() was fixed.