Split Custom Asteroids, using Custom Biomes as a template.

Unlike in Custom Biomes, asteroid configs need not be mutually exclusive. Inner- and Outer-system configs registered separately because they have different compatibility requirements.
Naming convention proposed in #225.
Renamed new .ckan files to .netkan
Prepared for v1.2

The next release of Custom Asteroids will have both asteroid populations (what is currently required) and asteroid compositions. These should probably be treated as seperate "data" dependencies.
Changed files to UTF-8.
CustomAsteroids: Fix byte order marks
Merge commit 'bd7a0b6'

* commit 'bd7a0b6':
  CustomAsteroids: Fix byte order marks
  Changed files to UTF-8.
  Prepared for v1.2
  Renamed new .ckan files to .netkan
  Naming convention proposed in #225.
  Split Custom Asteroids, using Custom Biomes as a template.