Some properties were accidentally hidden for particle fluids.
- Made sure we show the Forces and Integration
sub-panels for particle fluids.
- Slightly re-ordered the sub-panels here, so that the same sub-panels
are at the top for Newtonian and Fluid particles.
- Separated the Fluid Interaction sub-panel so we can give it a unique
name.
- Removed lingering unnecessary 'Keys' label in the Keyed physics.
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