Add a way to use a fullscreen virtualkeyboard

On small display sizes the only option for having a virtual keyboard is to use a full screen virtual keyboard. This will occupy the whole screen and includes the TextField the user adds it's text to. The user should be able to mark/copy and paste in this TextField like in a TextField embedded in a UI and it should also use the same constraints as a normal TextField e.g. EnterKeyAction or the EchoMode.

Usually a fullscreen keyboard behaves like this:
1. When the user clicks into the textfield and virtual keyboard opens, the existing text is copied from the ui-textField into the virtual keyboard text field.
2. The user can add text, copy, paste etc. using the virtual keyboard
3. The user can either abort the input, or commit. On an abort() the text previously in the ui-textField should still be the same. On a commit() the text should be changed to the new text from the virtual Keyboard.

This task is about adding a way to let the user implement this and also make this fully stylable as all the other keyboard components