Initial dynamic weather support

[Lihis]

This has been work-in-progress (see Lihis/openrw#2) for a while and I will not have time to finish any time soon so I think it might be better to get this merged in its current state so someone can improve it at some point.

I have not tested this against latest main but I'll try to do it within few weeks or so.

Copy-paste from PR in my fork of the repo:

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Tasklist and some details:

• [x] Weather cycles according the weather list for GTA III.
• [ ] Verify is the above weather list same for:
  • [ ] v1.1
  • [ ] Steam version
• [ ] Rain droplets in rainy weather
• [ ] Weather can be controlled by opcodes and it behaves according them:
  • [ ] 01B5: Force next weather (see https://github.com/rwengine/openrw/issues/379#issuecomment-386902620). Weather does not cycle until released (via 01B7).
  • [x] 01B6: Force weather now; weather is immediately set to requested weather. Weather does not cycle until released (via 01B7).
  • [x] 01B7: Release weather; continue weather cycle from where it was.
  • 0251: Store weather; unused.
  • 0251: Restore weather; unused.
• [ ] New game:
  • [ ] Weather cycle starts from array index 0?
• [ ] Load game:
  • [ ] Clean save without weather cheats; weather cycle continues from the saved state.
  • [ ] "Dirty" save where a weather cheat used; weather does not cycle, weather is kept in the forced state.
• [ ] Write simple SCM for testing opcode 01B5.
• [ ] Did miss something? Yes/No: TBD