Fix for T61187.

Some properties were accidentally hidden for particle fluids. Here's a fix.

• Made sure we show the Forces and Integration subpanels for particle fluids
• Slightly re-ordered the subpanels here, so that the same subpanels are at the top for Newtonian and Fluid particles
• Separated the Fluid Interaction subpanel so we can give it a unique name
• Removed lingering unnecessary 'Keys' label in the Keyed physics