On fullscreen mode don't appear on mouse display

When Guake is on fullscreen mode ignores the "Appear on mouse display" preference.

How to reproduce:
- Have at least two display (for eg a notebook to an external monitor through HDMI).
- Start Guake:
- Change your mouse cursor alternatively between displays and press F12 repeatedly
- If it is in fullscreen mode: Will stay on the previous display.
- If it is in window mode: Will appear on mouse display.

No special output when doing this but yes before (see [attached file](https://github.com/Guake/guake/files/888857/Guake_Issue_928.txt)).

If this is the expected behavior _Appear on mouse display_ should warn about it and probably should have another preference checkbox to _Appear on mouse display **always**_.

I think this bug is not a duplicate of #607 where [@versusvoid](https://github.com/Guake/guake/issues/607#issuecomment-223942342) and [@alliefitter](https://github.com/Guake/guake/issues/607#issuecomment-283383585) mention this behavior.