Plotting style

[cdeil]

Currently we're using the default matplotlib plotting style:

IMO it's not very pretty we should adopt the Astropy plotting style (see here, but it doesn't show up because of Astropy Sphinx bugs, sigh) or define our own.
It's pretty easy to implement, se here and here how it was done in Gammapy.

I think there also was talk about a "dark style" for astroplan, but now I can't find any issue for that.

What do you think?

I've put the 0.2 milestone, but if someone wants to implement this today for 0.1, it should be possible.

[jberlanga]

We did talk about a "dark style", and I put that in the TODO section of all the plotting function docstrings, but it never did end up in an issue of its own.

Matplotlib is coming out with new defaults soon. Maybe we should wait until after?

[cdeil]

I haven't seen the new matplotlib style (other than the color map), but I trust it's going to be good, so am OK with us using.
But there's the issue that we want to support both matplotlib 1 and 2, i.e. our image comparison tests should work with either.
Probably the simplest solution is to define our own style (which could be just a copy of the default matplotlib 2.0 style)

I've mentioned this in https://github.com/astrofrog/pytest-mpl/issues/12 ... let's wait and see what @astrofrog recommends.