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

Sph properties

Once !159 has been merged in, this merge request improves the handling of SPH parameters by actually reading them from the YAML file and not simply using the constants from const.h

See merge request !160

Timed outputs

Fix to #161.

Also corrects the run script for the external point mass that used to regenerate the ICs every time. 

See merge request !163

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

Fix parameter file parsing for duplicate names

The parameter file parser now checks for duplicate parameter names within sections and standalone parameters. It also checks for duplicate section names.

See merge request !161

Removed an extra kernel_igamma from the rho_dh calculation

There was an extra kernel_igamma in the calculation of rho_sh which was causing an offset to equivalent Gadget-2 runs. 

See merge request !162