remove base_kernel_url
add InlineBackend.print_figure_kwargs

removes special handling of 'quality', in favor of passing arbitrary kwargs to fig.canvas.print_figure.

This lets people override the occasionally problematic use of `bbox_inches='tight'`,
and any potential future issue that might be solved by adding/changing kwargs to print_figure.
Some template static_url tweaks

- don't try to include version in static_urls that don't point to files
- use full static_urls (with extension) for backbone and underscore, so version can be computed

closes #5141
Simplify implementation of TemporaryWorkingDirectory.

Closes gh-5160
Don't introspect __call__ for simple callables

Closes gh-5164
remove mktemp usage

mktemp is insecure, by the time the generated filename is used someone
else might have modified it.
Merge pull request #5166 from juliantaylor/mktemp-remove

remove mktemp usage
Merge pull request #5163 from takluyver/i5160

Simplify implementation of TemporaryWorkingDirectory.
Merge pull request #5100 from minrk/base_kernel_url

remove base_kernel_url
Merge pull request #5147 from minrk/static-url-version

Some template URL changes
fixup
test select_figure_formats
remove InlineBackend.quality from whatsnew
add print_figure_kwargs to whatsnew
read InlineBackend defaults in set_matplotlib_formats
specify default bbox_inches in print_figure explicitly

to preserve legacy behavior for any direct callers
test display.set_matplotlib_formats

give set_matplotlib_close default close=True
remove redundant check for self.shell is None
generate supported formats in ValueError
remove websocket url

websockets should follow the kernel URL

(normal behavior is unchanged, only unused configurability is removed)