Add restyled widget addition control
Force widget-addition control to appear at end of widget list
Fix widget control margins
Prevent clicking on 'Add a widget' from selecting
Add widgets using new panel. Props @shaunandrews
Toggle visibility of old single-widget in new panel
Add widget icon
Allow widget icon url to be filtered
Prevent widget filter from appearing when panel is closed
Prefix sidebar sections with 'Widgets:'

/cc @shaunandrews
Fix live filter
Add widget icons, including default icon
Restore fix to live filter (ab7d7a1)

/cc @shaunandrews
Merge branch 'master' into new-widget-addition
Merge branch 'master' into new-widget-addition

Conflicts:
	widget-customizer.js
	widget-customizer.php
Fix typo s/Wodgets/Widgets/
Fix jshint errors
Add keyboard accessibility for adding new widgets
Merge branch 'develop' into new-widget-addition

Conflicts:
	widget-customizer.js
	widget-customizer.php
Prevent tabbing from toggling add-widget panel