[gnome-software] (15 commits) ...Merge branch 'category-app-tiles' into 'master'

[Milan Crha <mcrha src gnome org>]

Summary of changes:

  bbc6d98... gs-app-tile: Drop gs_app_tile_new() as it’s an abstract cla
  6529c91... gs-app-tile: Add a GsAppTile:app property
  3fbf273... gs-app-tile: Simplify constructors of derived classes
  e1a777a... gs-summary-tile: Modernise GObject property usage
  09a8831... gs-summary-tile: Drop support for custom CSS
  9fd6a62... gs-app-tile: Add a CSS name to the widget
  29bbff1... gs-summary-tile: Add a CSS name to the widget
  65292cf... gs-app-tile: Simplify notify handling
  fa0f777... gs-app-tile: Don’t unnecessary destroy and recreate idle ha
  01979b6... gs-summary-tile: Minor code formatting tweaks
  6c40f96... gs-summary-tile: Add rounded corners
  d5d1b61... gs-category-page: Use GsSummaryTile instead of GsPopularTil
  1c0510c... gs-overview-page: Use GsSummaryTile instead of GsPopularTil
  9794b42... gs-popular-tile: Remove GsPopularTile as it’s now unused
  03e33c3... Merge branch 'category-app-tiles' into 'master'