Kwplot

Added
* Add `show_ticks=False` keyword argument to `imshow`
* Add `phantom_legend` function
* Exposed `render_figure_to_image` function
* Added `__main__` script to show a normalized image.

Added
* `kwplot.autosns` for auto seaborn convenience.

Fixed
* Fixed potential crash in autompl on some systems with conflicting PyQt5 and
python-opencv libraries. This involves falling back to agg if there *might*
be a conflict. The environ KWPLOT_UNSAFE=1 can be set to use the old behavior

Added
* Added "force" kwarg to autompl, which will change the backend and prevent
future non-force autompl calls from changing the backend.

* BackendContext - a context manager for matplotlib backends. Primary purpose
is to allow the user to ensure that the agg backend is used in certain
places.

* `mpl_draw.draw_points` - draws 2d points

Fixed
* Bugs in `plot_matrix`