AppStream, Discover and metadata

[Jonathan Riddell]

Discussed this briefly at Munich sprint.  The packages in
ppa:ximion/packagekit are fine to develop against and if Plasma 5.5
gets put into wily those packagekit and appstream packages will be
used for that.  For xenial the packagekit update has again been
rejected and if that stays the same then it might need a second
packagekit in the Ubuntu archive but that's hardly idea so Rohan is
going to bring it up on ubuntu-devel.

So a qapt+appstream backend might be nice if packagekit doesn't get
sorted but if it's too much work don't worry about it because the
problem should be fixed in Ubuntu.

Jonathan