[gnome-software] (10 commits) ...GsApp: move local package icon loading here

[Kalev Lember <klember src gnome org>]

Summary of changes:

  669391e... Don't include gs-cleanup.h from other .h files (*)
  788f864... Define a cleanup function for gs_plugin_list_free (*)
  d5c88a6... dbus helper: Port to gdbus-codegen generated helper
  02fb18b... Factor out gs_app_show_url
  93d467e... Add a common base class that all shell pages derive from
  643f526... trivial: app row: Remove a redundant condition
  c8e407b... app row: Don't show ratings for local and missing apps
  4717aaf... app row: Don't escape missing description
  f66eb29... plugin loader: Re-refine apps after install / remove
  3a2b3af... GsApp: move local package icon loading here

(*) This commit already existed in another branch; no separate mail sent