Simplify the gravity potential calculations for M2L and M2P since the softened case should never take place any more. REplace the calculation by an error message.

Improve the M2P criterion to make sure we don't interact a particle and a multipole if the distance between them is less than the sofetning length (spline truncation radius)

Gear pressure floor

See merge request !811

Black holes repositioning

See merge request !876

GEAR: add star formation with correct eagle logger

See merge request !879

removed dx_max from space.h since it's not needed anymore

See merge request !880

SWIFT can not read DM background particles from the ICs using the particle type 2. These are treated as regular DM gparts after that.