[Users] Feature request: allow usbtablet and vram config via UI

Allow for a usbtablet input device to be enabled and used. Perhaps via the console configuration UI for a VM in the admin and user portals. -Highly useful in the event that a guest OS does not have the spice agent loaded nor is it available for said guest OS. -Also in the case of guest OS that simply does not want to work and play well with <input type='mouse' bus='ps2'> - All Operating systems since ~1998 understand <input type='tablet' bus='usb'/> and will deal with mouse events in absolute mode Allow for vram and vram_ size to be configurable for CIrrus(VNC) and QXL(Spice) console types. - Default VRAM sizes are not enough to allow for larger resolutions at times. - Especially the case in multiple monitor SPICE, fullscreen, or VNC consoles The above can be altered via VDSM hooks however this is rather painful. Additionally these options or similar are configurable in other competing solutions. - DHC