This seeks to remove the "_" from the key presses of snapshots and inline
runs in the documentation. The "_" no longer does anything, but got legacy
reasons at the moment we can't actually allow "_" to be an input to a
"faked" keypress in the docs and snapshots.
Removing these clears the way to letting "_" have the same status as any
other character.
See #1994.
* Change the title of some widget references to their class names
The widget reference index had a slight mixture of widget title styles, some
being their class name, others being "written English" type titles. This
settles on the titles always being the class name.
* Add a link to the ContentSwitcher to the widget gallery
No screenshot for this, on purpose. By definition this widget isn't visible,
except via other widgets that it's enclosing and handling.
* Have mkdocs watch the main nav file
* Mark the content switcher off the roadmap
