Provide feedback while loading in ResultList

[crantila]

Sometimes there is noticeable lag between when someone clicks the "Search" button (or chooses to go to the next page, etc.) and when the results show up. To help users know that their search was submitted, we should show a progress bar or something.

[crantila]

Note that this will have to work both when the ResultList is waiting for search results, and when it's waiting for a collection from LocalStorage.