Replace the region paradigm with just painting textures

[stscieisenhamer]

Issue

Currently, regions are separated by a conceptual concept, such as "disk", "gas", or "bulge". This paradigm has proven to be limiting. Instead, simply produce regions directly related to the texture desired to be used.

GUI-wise, this is not much of a change. However, this will impact the 3D modeling API and algorithms.

Implementation

• implement texture-only gui + rendering see issue Create regions based solely on available textures #13
• Remove vesitges of the conceptual regions
  • How to identify regions that have special functions, such as Bulge and remove_star.
  • Auto mask creation: where would the new masks go?