WebUI page that shows files that can not be read to aid setup debugging

[haku]

when a file can not be read, Watcher puts in it in a DelayQueue and periodically retries until the file can be successfully read. it also logs which files it is waiting for, but this is awkward if there are lots of them so might be helpful to provide a UI page that lists these files.

questions:

• who has access to view this list? maybe somehow filter list based on access permissions the items will have once they can be read? or create some new permission for this?