Keyboard. Add highlighter for 'Enter' button

[melofon]

To be able to add Enter to the keyboad codes file it's needed to replace Enter with some other key. I.e.:

        var key = values[0]
        if key == 'enter':
            key = char(10)
        key_dict[key] = Vector2(int(values[1]),int(values[2]))

This should be done in 'keyboard.gd' file and having that done, the 'enter' key can be added to the 'keyboard.txt'.