Non-job listings

[jace]

Hasjob needs the ability to have non-job listings like the Headstart Higher announcements (or event announcements). These should be yet another status value, and the page UI should change subtly to indicate their status:

1. Stickie is a different colour
2. No "Apply for this position" section
3. Job type and category are special non-public values
4. No "Report this" in the sidebar
5. Recruiter notice replaced with a "special announcement" or "sponsor listing" notice

[jace]

Implemented in c6a85bd without UI (to mark a listing as an announcement) as it is expected to be a rarely used feature.