Packaging update to get read for Wayland Nemo

I have splitted nemo-mobile-session in three subpackages:
-common: has files needed by both configs (room for future improvement here, as I'm not sure which env vars and which files are X11 only)

- xorg: keeps x11 specific configurations. Currently empty, but it will host x11 specific files. Some files from -common could be moved here in the future

- wayland: Wayland specific files, currently only compositor configurations

It has been tested on an updated X11 image using "zypper dup --from" to bypass the vendor check.

Also qt5-plugin-generic-vboxtouch support has been added (for the Wayland configuration only), and it's been set as a requirement to the -wayland package