Added name of parameter file to error messages.



See merge request !170

Conflicts:
	src/task.c

Task plot improvements

I have updated the plotting script and the output of the task data such that we can now have the full information for a given time-step and not just the last call to `engine_launch()`. This means the `drift` tasks will now be included in the plots. They will also include the single-core part where the cells and tasks are reconstructed. 
The start and end time as well as the CPU frequency are dumped in order for this to work.

Also, added a cosmetic change to the output for the case where a snapshot gets dump. 

See merge request !166

Better output of wallclock time when writing a snapshot. Slight improvement to the task plotting scripts

Better names for functions

This closes #143.

I have also updated the names of the functions in runner.c to stop linguistic problems between "dog host" and do ghost" for instance. 

See merge request !165

Time-step synchronisation

Ok, this is the final fix to #93. Particles are not allowed to move to a longer time-step unless we are currently doing a time-step of that size. That will prevent particles from being completely all over the place in the time-step hierarchy.

It wasn't physically wrong until now, just not efficient and very confusing.

With this fix in place, there will always be a time-step every so often where all particles are updated. 

See merge request !164