Merge pull request #1918 from mtwebster/adv-button

cinnamon-settings: Replace gear, button for advanced mode with link button
Refactor applet module code, expand to desklets
Add extensions
Missed a change
cinnamon-settings:  some fixes, strings, confirmation on removal of
more than one instance
Add error popup when server communication fails, don't just hang there.
Show http error when downloading fails
disable webkit for now, as we're not using it
Focus search box on startup
Allow filter to be cumulative - showing active, inactive, or all at once.
Add an "Active" label to help distinguish between active and inactive items
Fix problem with checking an applet while search filter is active
Whoops... install to the right folder
Fix extensions code
Add functionality to store the edited-date, and use it to compare spices
against installed applets to detect when an update can be done