Applied the changes expected in the commit 388c4ea3 without all the bad stuff it also included. Code formatting.

This reverts commit 388c4ea3.

Make sure we correctly collect the time-step sizes in the case where we only have external gravity and no self-gravity.

When running star formation and feedback (not yet over MPI), make sure the star sorts are correctly updated once a star has been formed.

If we ran out of particles when creating a star, do not attempt to copy the properties of the gas particle to the star.

Applied code formatting tool and explicitely documented the fact that the EAGLE floor assumes neutral primoridal gas.