Handle reloading state when streaming Rapid Diffs

We should handle reloading state when streaming Rapid Diffs after we change whitespace or inline/parallel setting. The process works like this:

1. Click to change a setting in the diff view settings
2. Wait for diffs streaming request to respond
3. Stream diffs on the page using that request

A visual feedback should occur in between the time when we switch the setting (1) and actually render new content on the page (3). Right now we simply close the settings dropdown and there's no visual feedback that something is loading. After we got the diffs streaming request we'll see loading progress in the file browser.