Test more backends and handle resizing for interactive backends

[lukelbd]

When either of the width or height dimensions are not passed to the figure, the proplot tight layout algorithm resizes the figure. This means whenever the figure has to be "re-drawn", as with expanding a popup window, the algorithm will try to snap the window back to match the old figure size, resulting in weird/jumpy behavior.

Had two ideas to fix this.

1. Make all backend window sizes explicitly locked. See this thread for ideas.
2. Have set_size_inches update the underlying geometry_configurator settings (see Replace "panels" with EdgeStack, permit working directly with add_subplot/GridSpec #50) so that "width" and "height" are both fixed, and also make the axwidth, axheight, and aspect settings modifiable (also rename aspect to axaspect?). Internal calls to set_size_inches can pass a keyword arg like lock=False that prevents updating geometry settings.

Leaning towards 2. Also, while I'm at it, I can also do a more rigorous test of how automatic figure resizing interacts with the various backends.

[lukelbd]

Some backends also have a problem with the automatic offset of row/column labels and "super" titles. Thought I fixed this before but evidently not. See this example:

[lukelbd]

This needs to be higher priority. It's currently causing bugs when nbsphinx executes the cells from the documentation notebooks on RTD. Trying for a workaround.

[lukelbd]

#46 (#50) will probably fix this. Super titles and row/column labels will be implemented with the same API used to draw outer colorbars and legends.

[lukelbd]

Ended up fixing the tight layout bug and making the algorithm more robust to different backends for v0.1.3 (commit: 67221d1). But manual resizing with interactive backends is still an issue -- see #76 for further updates.