WebLinkback: faster email notification

 * Improves database layer to send email notification faster

 * Extends regression tests for this improvement

 * Applies minor clean-up
WebLinkback: faster deletion of linkbacks on blacklist

 * Avoids redundant creations of blacklist
Merge pull request #27 from egabancho/patrik-master-faster-weblinkback

Master faster weblinkback