Move POST functionality out of jobpost view handler

[jace]

Hasjob's views.listing.jobdetail view handles both GET and POST requests, and with the latter performs maintenance tasks such as the report form (user-facing), reject form (admin-only) and moderate form (admin-only). These three views are handled by jobdetail and not a separate view purely for reason of a legacy choice.

Each of these three needs to be moved out into a separate POST-only view with its own route that does a 303 redirect back to the main page. There is no reason for jobdetail handling POST queries.