Reduce duplicate code in PortraitKeyboard.qml and LandscapeKeyboard.qml

The files PortraitKeyboard.qml and LandscapeKeyboard.qml contain a lot of duplicate code.

Changing these files is sometimes required when adding new features/fixing bugs and one can easily forget to modify both files. So I'd propose moving the key definitions to another file (where possible) and sharing them between the two *Keyboard.qml files.

Furthermore, we have the color definition "#DD4814" in there quite often, so that should be moved to a separate property as well, which should then be accessed by all key definitions.