Still tweaking icons in sidebar.
Add extensions/vendor to Filesystemadapters.
Working on "Config" and "read me" buttons.
We don't need to edit anything in the extensions/ folder.
Working on #1634, #1635: config and read me for extensions.

Pinging @GawainLynch, very much a work in progress.
Replacing some "trash-o" icons with "trash"
Added icon to uninstall button for extensions.