[Menu applet][Search Web] Make strings translatable in search item
[Menu Applet][Search Web] Store search strings in gsettings
[Menu Applet][Search Web] Let applet respond to changes in gsettings
[Menu Applet][Search Web] Fix DuckDuckGo search path
[Menu Applet][Search Web] Show icons in search items
[Menu Applet][Search Web] Allow separators
[Menu Applet][Search Web] Add separator description to gsettings schema