Remove PGPLOT dependance

[martinjohndyer]

Replace with something easier to install.

[martinjohndyer]

Just to keep track of things, here's a quick survey of the current uses of PGPLOT in the package:

• reduce is the main script that still relies on PGPLOT for speed. This will need replacing with something equally fast, see Create list of possible plotting libaries #167. The actual code is in the reduction.py module. This will be the main task, for both the light curve plots and image displays.
• rtplot, the real-time plotter, is these days pretty much entirely replaced with the matplotlib version nrtplot. If we're removing PGPLOT then we can remote rtplot entirely (but perhaps add an alias so both names direct to the mpl version).
  • Will need some checking if there are any features in rtplot that never got moved over.
  • Suggestion to go back and check some very early ULTRACAM runs to make sure nrtplot is fully backwards-compatible.
• aligntool, the actual alignment fit plots are in mpl but it uses PGPLOT to display images. Should be simple to replace with pure mpl.
  • Some test images would be useful, @vikdhillon to provide
• ftargets, another case that still uses PGPLOT to display images.
  • A bit more complicated in that is plots various apertures, but again the existing mpl code should be fine.
• hplot has both PGPLOT and mpl as options, in this case we can just strip out the PGPLOT parts.
  • Again, making sure we don't lose any useful features, like the profile fitting (added profile fitting to hplot #114)
• redanal imports PGPLOT (and matplotlib) but doesn't actually do any plotting??

I think that's everything, although the use of * imports makes it a little annoying to search. Once the above is all done then we can finally remove the pgp module and the dependency on trm.pgplot.