Removed support for the defunct option to run VELOCIraptor every fixed number of steps rather than at a fixed time.

Make all the EAGLE examples run with gravity, cosmology and stars switched on. Make them dump more snapshots.

Set the compression level to 1 for the basic examples. 4 does not improve things and is just slower.

This reverts commit ccf5f553.

Improve the way we define the time of the first snapshot and statistics in cosmology and non-cosmology modes.

Changed VELOCIraptor interface to pass output file name at invoke time instead of at initialisation.