Settings upgrade

[Helium314]

The current settings have grown enormously, and looking at the number of very specific feature requests, they are likely going to grow even more.

An upgraded settings screen should not just be a better organized version of the current settings but also address some shortcomings that arise from using the AndroidX Preference library, i.e. it need to be re-written almost completely.
What should be improved:

• arrangement of settings
• style of some settings (especially the dialogs are often not really great)
• add a search field for easily finding settings (across settings screens)
• add a text field for showing the keyboard everywhere
• better languages & layouts section in general, and specifically
  • allow changing layout when use system langauges is enabled
  • allow setting a complete set of keyboard layouts (functional keys, symbols, numpad, ...), instead of just a single main layout
  • popup key order and hint source should then also be per layout, and not per language
  • there is already too much stuff in the dialog, and when adding even more settings it should be replaced with a separate screen

Not all of this will be implemented a once, but knowing what else needs to be done is useful for planning.