A new option allow to choose a secondary layout, the switching key is
placed on the top edge of the space bar.
The "Programming layout" option was basically doing that but it was
possible to choose from a few layouts only. It is improved and renamed.
The 'LayoutListPreference' allows setting the string for the first entry
but otherwise share the rest of the array.
Add nice icons from materialdesignicons.
Bring back the "Vibration" option.
The duration option isn't added back because the vibration settings are
still handled by Android. In fact, the option has no effect if the
vibration are disabled in the system settings.
This partially reverts commit ef03dfed5c.
