[qmf-notifications-plugin] Removal all notifications items if there's more than one item published.

In a error case that more than one notification item gets published
by the same app(messageserver5) we clean eveything, this is a rare
condition, only happens in case of a failure.
Merge pull request #14 from nemomobile/notifications-removal

[qmf-notifications-plugin] Removal all notifications items if there's more than one item published.