added colorsetting function

[jo-mueller]

Fixes #64

I added a function to the plot base class that applies the functions pointed out by @haesleinhuepf in this discussion. The function can then called whenever the self.axes object has been created in any plot class that was derived from the main class.

I put it as a draft PR since there are no tests yet. Also I think that it could be mentioned in the contribution guidelines that new widgets should call this method after self.canvas.figure.add_subplot() has been called.

Let me know what you think :)

[dstansby]

A couple of minor changes, and a suggestion for iterating through the spines. Otherwise looking 👍 (and sorry about how long it's taken me to get to this, if you want me to finish this off just let me know!)

[dstansby]

Ooh also a rebase would be good to check that pre-commit is happy!

[jo-mueller]

Hi @dstansby ,

thanks for the feedback, I incorporated your suggestions. The last commit was me not realizing that set_tight_layout() had been deprecated when I rebased my branch ^^"

PS: I edited the PR message so that both #36 and #64 will be closed by this PR as they both address the same issue.

[dstansby]

Looks 👍 - not sure this does fix #36, as there hasn't been a matplotlibrc file added. That's fine for now, but I'll make sure that issue doesn't get closed when I merge this 😄