Scaling plots

Added code to create an extra output file that contains timing information for every timestep. The output file also contains a header that includes: branch, Git revision, compiler version, number of threads, number of MPI ranks, hydro scheme, hydro kernel, no. of neighbours and eta.

Added two parameters to cosmoVolume.yml that are used to create a file for the energy output per timestep and timing information.

Also added a python script that plots scaling results for varying numbers of threads and data series.

See merge request !197