place window number top-left
deferred thumbnail-clone creation
use my special method for determining whether an icon belongs to the current workspace when deciding on icon size
more icon sizing
icon positioning, again
thumbnail positioning
window-number label positioning, once again
only defer drawing the thumbnails behind the icons, not the drawing of the icons
defer thumbnail drawing using idle_add
check for deferred action happening after removal from stage
reassign keyboard shortcut for saving current config, add an alternate context-menu shortcut

It appears that Shift+F10 is a semi-standard context-menu shortcut, so let's
use that, since some keyboards lack a context-menu key.

That means that the shortcut for saving the current configuration had to
change, and I chose Shift+F3 instead.
Merge branch 'dev'
last-minute overview of README