[Extension.js] Cleanup
[Desklets] Revamped desklet manager for consistency with applet manager
Merge pull request #1589 from dalcde/desklet-revamp

[Desklets] Revamped desklet manager for consistency with applet manager 
[alt-tab] Show windows from all workspaces. Highlight "urgent" windows.
[sound applet] Cleanup after removing a player.
[popupMenu.js] Simplify connection management.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	js/ui/main.js
[alt-tab] Show windows from all workspaces. (4) Add a separator between windows from different workspaces.
[alt-tab] Show windows from all workspaces. (5) Do not initial-select a window belonging to another workspace.
[alt-tab] Show windows from all workspaces. (6)

Add the desktop window as a placeholder if no other window can be found for the currently active workspace.