Cache downloaded whitelist data and provide manual refresh option
For all of its existence, if the browser was not online when Smart Referer did an whitelist update, the given whitelist entry would end up effectively being ignored until the next refresh.
The only ways to trigger such refresh was to either reload the extension (by disabling+reenabling it or restarting the browser) or add and remove a bogus whitelist source in the options. This should be improved as well.
Additionally it would be grand if the whitelist contents were persisted between extension restarts, so that the cached data is available immediately while the update process is still ongoing.