ext/gui: remove most of it, moved to qvm-start-gui tool...
ext/gui: remove most of it, moved to qvm-start-gui tool...

...in core-mgmt-client repository. qubesd isn't the right place to start
GUI applications, which will be even more important when GUI domain will
be something different than Dom0.

QubesOS/qubes-issues#833

marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin