New button-styles:
 - `change-view`: Highlighted like `special`,
   but with a border at the bottom.
 - `character-group`: Like `change-view`, but with less highlighting.
 - `placeholder`: Less contrast to the background and does not visually
   change when pressed.
 - `subtle-highlight`: For highlighting commonly used characters
   in accent-views, for example.

New layouts:
 - Portuguese
 - Slovenian
 - Turkish (F-layout)
 - Turkish (Q-layout)

Remade layout:
 - Portuguese (Brazil): A view for accents has been added.

Changes:
 - The new button-styles are used in the available layouts,
   where appropriate.
 - The top rows of the terminal-layouts are a little taller.
 - Squeekboard will choose the wide shape of layouts, for more displays
   in horizontal orientation.
 - Highlighted buttons now show visual feedback too, when pressed.
 - Many layouts have been adjusted,
   so that those change their form less when switching views.
 - Various small issues have been fixed, to make layouts mor...