Nifty clutser solution

Adds a plotSolution.py for the nIFTY cluster.

Current status:

Current issues:

• Unclear what value of mu to choose
• Possibly linked to this, we get a temperature profile very different to other published codes
• We seem to produce DM cores? Unclear whether this is a plotting issue or a real issue
• unyt reports g / cm^3 as it has no in-built solar mass unit

Current successes:

• Entropy profile looks very similar to the published one for ANARCHY-PA (Gadget2)
• Gas density profile and image looks similar to previously published work

Ongoing work:

• I have a minimal run going.
• We should test with some kind of sub-grid.
• Extract plotting information from the paper and add to repository.
• Make the cluster centre finding more user friendly, currently have to edit script.