[email protected]: Rework layout, use cupsd dbus notifications (#13674)

for printer and job info.

We've long used the cupsd notifier to tell us when to run shell
commands that collect job and printer data, but this data has been
provided by these notifications all along, and it much more relable
than parsing shell output (which can change unexpectedly with new
versions or on different distributions).

- Stop using shell commands to gather job and printer information.
  They're now used only to cancel or prioritize jobs, and for basic
  printer discovery at startup.
- Organize jobs under each printer when multiple printers are
  available.
- Provide access to individual printer properties.
- Move the 'Printers' menu item to the context menu, except when no
  printers have been discovered.
- Use job/printer state-reasons for reporting abnormal conditions
  such as no-paper. Icon changes accordingly.
- Cancel-all avoids permission issues for some users by cancelling
  jobs individually (credit @hans-fritz-pommes)
- Cancel prompts use native Cinnamon dialogs.
- Some translatable strings updated, mainly for case consistency.

Author: mtwebster

data/theme/cinnamon-sass/widgets/_menus.scss

@@ -137,6 +137,11 @@ $menuitem_border_radius: $base_border_radius * 1;
   }
 }
 
+// printer applet menu item table
+.popup-printer-menu-item {
+  spacing-columns: 8px;
+}
+
 // Used in window quick list and power applet
 .popup-subtitle-menu-item { font-weight: normal; }