[gnome-software] (18 commits) ...Merge branch '1147-icons-refactoring' into 'master'

[Philip Withnall <pwithnall src gnome org>]

Summary of changes:

  ce5c8ab... gs-app: Return NULL from get_icons() if no icons are set
  9d8e659... gs-app: Print icon width in debug information
  321e754... gs-app: Sort icon array by size
  2ee47d4... gs-app: Split out functionality to remove all icons
  339e1ef... gs-utils: Clarify some negative flag conditions
  1f2165b... gs-utils: Drop support for reading cache from /usr/share/gn
  e28b24c... gs-utils: Make creating cache directory optional
  b777fa5... lib: Add GsRemoteIcon as a GIcon implementation for remote 
  b8818da... gs-plugin-icons: Stop adding custom theme paths for stock i
  f49a740... lib: Port GsApp to use GIcons rather than GdkPixbufs for ic
  52fe596... lib: Drop gs_app_load_pixbuf() and use GIcons instead
  c605dfb... gs-overview-page: Tweak empty page handling
  8fecc6e... gs-overview-page: Hide apps with low-res icons from feature
  c58cd3a... gs-flatpak: Export both sizes of icons from flatpak bundles
  5c8987f... tests: Test key colours using a different test app
  296fb05... appstream: Fix some icon leaks in gs-appstream.c
  e7cfa82... gs-details-page: Allow fallback sizes for icon
  5db3df0... Merge branch '1147-icons-refactoring' into 'master'