* offer removal of no-longer-supported apps
* improve countrymirror detection


UpdateManager.Common.aptsources.py:
- make the distro detection in sources.list more clever by using the
  origin informaton to avoid adding full uris to (unofficial/internal)
  mirrors 
- make it possible to inherit the mirrros from a ParentSuite (for
  the childs)

Misc:
- have a common error dialog readymade and rib out all those 
  GtkMessageDialogs
- add download size to treeview
- add /etc/apt/software-properties.d dir where the user can
  install matchers and templates
- handle cases like "deb http://bla/ dist sec1 sec2 # comment" 
- rework the add channel/cdrom dialogs
- d'n'd for key files
- use one row per section and not one per channel in the treeview
- sort the sources by dist
