findSvc angularjs service now can search a folder in a list of folders, instead of searching in the list of folders stored in the root scope.

If no list is passed to the service, the default behavior is still to search in the root scope, so this shouldn't break anything.

This will enable us to search in the list of folders returned by the server. This will be necessary to change the behavior when loading feeds: instead of just replacing the list of folders in the root scope with the folders returned by the server (which will replace all folder objects with new ones), only new folders will be inserted in the scope (and folders in the scope not present in the list returned by the server will be removed). This way folders that have not changed will not have the object that represents them replaced by a new identical one.
When loading folders from the server, insert only new folders, and remove any folders not returned by the server.

The old behavior was simply to replace the full list of folders with the one returned by the server. This meant that even for folders that had not changed, the object representing them in the scope was replaced by a new one. This caused complications keeping track of which folder was open in the sidebar at a given time.

With the new behavior, folders that haven't changed will not change in the angularjs model layer. This makes more sense, even if the price to pay is a slightly more complicated logic.