default applications for 15.10

[Tim]

Hey All,
   We have been saying for a while we would switch the default media apps to the new GNOME ones once they mature, rather than inheriting the
Ubuntu defaults. These apps have now had a few cycles to brew up and are a much better fit for the GNOME DE.

The main changes would be:
 - shotwell replaced by gnome-photos
 - rhythmbox replaced by gnome-music
-  Possibly add the getting started guide (but english only, its too big to fit on images otherwise)
- Infrastructure for gnome-software is not ready in debian/Ubuntu so that will come later likely in one of the 16.x releases

What does everyone think? Note this mainly only affects new installs, upgrades will keep the old apps also.

Tim