The 'accent_slash' was missing in the extra keys setting.
Allow to type more latin letters "with oblique stroke" or "with stroke"
that visually have an oblique bar, that were not added to 'accent_bar'.
The key enable caps lock immediately. It does nothing if caps lock is
already enabled.
It is not present on the keyboard by default but a place is defined on
every layout, top-right of the shift key. It can be enabled in the
settings.
The icon is from materialdesignicons.com.
The Fn+switch_numeric shortcut might be hard to discover or too slow for
heavy users.
A location is allocated for the key so it has a consistent placement.
Allows to add more keys to the keyboard from a predefined list.
The implementation doesn't use MultiSelectListPreference because it
doesn't seem possible to change the item layout to properly show the
rendered symbols.
