Custom Launch Music for Each Planet

[Mythril382]

To-do:

• Add (h)json support.

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[Anuken]

I don't think the three music categories are good enough of a system to warrant being configurable per-planet.

[MEEPofFaith]

Custom ambient/dark/boss music for each planet when

[Anuken]

The definitions of dark/boss are pretty vague right now, so I think planets should define that themselves. Maybe a custom handler of some sort?