Support KSP 1.10 comets in Custom Asteroids

[Starstrider42]

KSP 1.10 adds comets to the stock game. Custom Asteroids should be able to generate such comets itself, replacing the asteroids-on-cometary-orbits approach of previous versions.

Specific requirements:

• Custom Asteroids must still be able to work with asteroid packs written for previous versions of KSP or Custom Asteroids.
• The comets provided by the "standard" config packs must emulate stock comets. This means changing the properties of the existing oort and innerComets groups (which roughly correspond to long- and intermediate-period comets in the new system).
  • Emulating the stock size distribution (sizes F through H, plus I) requires Size distributions #6.
• Comet-related contracts must be able to recognize new comets created by Custom Asteroids, whether or not they're from a group that emulates stock comets.
• I'm not sure yet how much interaction the new code should have with the stock COMET_ORBIT_TYPE configs.
  • ModuleComet and CometVessel almost certainly depend on these blocks, so they must be used at least for comets' physical properties.
  • Custom Asteroids provides more flexible orbit specification than the stock configs.
  • On the other hand, Custom Asteroids does not (yet) support custom sampling experiments for asteroids of the same part type. Having each type of object be its own part is clunkier than the stock approach, but more powerful (since it naturally handles resources, textures, etc. as well).
• Sentinel support for comets need not be handled yet (see Sentinel Telescope creates non-CA asteroids #35).
• It would be helpful if the Custom Asteroids code and configs could gracefully revert to the old behavior for KSP 1.9 and earlier, but this would require Custom Asteroids to create a substitute PotatoComet that would not be a drop-in replacement for the real thing (different modules). This seems like more trouble than it's worth.

[Starstrider42]

@DMagic1, this issue may interest you, since IIRC some of your asteroid experiments assumed the existence of CaCometActive.

[Starstrider42]

Backward compatibility with KSP 1.9 is impractical; even just recompiling the current mod against KSP 1.10 gives lots of exceptions when running on KSP 1.9. This does not prevent compatibility with old configs, of course.