(Bug 2642) Add action links to OfficialPost notif

Refactors LJ::Event::OfficialPost to use LJ::Event::JournalNewEntry.
Adds "Reply | Link" to DW inbox notifs of official posts.
Adds "Leave a reply to this entry" to all notifs of new posts.
Merge pull request #521 from kaberett/bug2642-official-post-comments

(Bug 2642) Add action links to OfficialPost notif