The new script makes sure that strings files don't contain obsolete
strings but also ease the job of contributors by adding missing
translations as comments.
A Github Action ensures that translations stay in sync over time.
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.
