Merge branch 'timed_outputs' into 'master'

Timed outputs

This implements the improvement #142.

The time of the first output and the time difference between subsequent outputs can be specified in the parameter file. So no dumps after a fix number of steps any more.

Users can also specify a unit system for the snapshots. That gets passed along to the routines dumping the snapshot. 

I have updated all the YAML run scripts as well.

See merge request !159