Rework Custom Fuel tank series of parts to enable free-scaling of the diameter.

TODO:

• Testing... testing.. testing.
  • Test new texture pack stuff; unsure if it works at all; unfortunately, will need to manually delete the stuff after merge...

DONE:

• Add current nosecone/end-caps to mount definitions
• Add tech limit controls to length and diameter
• Mostly new module code based on custom-upper stage code to allow for free-diameter scaling and better model asset handling
• Add half-height increments of all existing tanks
• Update texture set functionality to be less verbose
• Add new tank models to texture sets
• Combine tank textures into a single texture, and combine meshes into a single mesh. Much improved asset handling, and easier splitting of texture sets into specific packs.
• Add bottom fairing support, including 'skip-a-node' functionality.
• Add custom texture-switch support with separate top/main/bottom texture-switch options
• Re-add in multi-node support
  • Add in check for if mount can be enabled based on current # of active nodes and attached parts.
• Fix up models to not appropriate a model that is in use already by the other cap; need to recreate every model, instead of trying to re-use.
• re-export to Unity, rename flag-transforms for conformity in unity, and re-export from unity.
• Add back in the rest of the cap definitions for the various adapters/mulicouplers
• Fix - Resources do some strange stuff; MP should not have the same quantity as LF (differing densities I believe)
• Fix - In-editor part-mass display