"Open website" should work for feeds that don't provide websiteURL

We can use the host part of feedURL in such case.
Remove dead code
Convert TagList.refreshTags() to use a task
Remove delay of hiding progress bar when refreshing is done.

The dalay is unnecessary now that we use a CSS transition
when hiding it.
Simplify code branches in StorageInternal.changeFeedProperties() a bit
Random code cleanup