Group submissions of requests to operations queue.

This is a follow-up on issue #348 : grouping the requests submissions greatly reduces the number of notifications being posted when the operation queue switches between empty and non empty state.
Merge pull request #354 from barijaona/bugfixes

Follow-up to issue #348 : group submissions of requests to operations queue.
added a test URL with an anchor for issue #351
Merge branch 'master' of github.com:josh64x2/vienna-rss