Add anti-spam filtering

[keathley]

We need to add anti-spam filtering for postings. The easiest thing to do is just to hook up rakismet with our JobPosting model.

[t-richards]

If a job posting is determined to be spam by the external service, should it be rejected outright (no save, no nothing)?

Alternatively, we could allow the posting to be saved, but require an admin to manually "approve" the posting before it becomes visible on the frontend. This is a tiny bit more complicated development-wise, and requires time investment from admins to manually moderate flagged postings.

[juzten]

I like the idea of admin approval if the service thinks the post is spam. We would also need to limit the number of posts by IP address otherwise we will be in the same boat, just on the admin side.

If people don't want to do the admining, I don't mind at all being the person who verifys and approves or deletes posts labeled as spam.

[t-richards]

Fixed in 8342c632fe2de4bedede0188134ad74d37b2a790