Remove prominence.

Add a migration to remove the unused column 'prominence' from
info_request_events, remove validation of prominence, remove unused
InfoRequestEvent.user_can_view? method. Remove references to
InfoRequestEvent.prominence.
Re-annotate models with database fields
Add prominence to incoming message.
Add response_event helper

Add a convenience method for getting the 'response' event associated
with an incoming message.
Refactor correspondence template into partials.
Rename method to make it a bit more generic

A super user will be able to see all hidden things, not just requests.
Add a method to ask whether a user can view an incoming message.
Refactor common logic about prominence and access.

Move it into the Ability module.
Refactor some common setup steps in integration tests into a DSL.

Add a failing test for what should happen on request hiding.
Add messages for hidden and requester_only states.

Different messages for normal user, requester and admin user.
Adding prominence_reason to IncomingMessage.
Add prominence reason.

Conflicts:

    app/views/request/_incoming_correspondence.html.erb

Conflicts:

    spec/integration/view_request_spec.rb
Remove unused hidden correspondence template.
Don't index hidden and requester_only incoming messages.
Move outgoing message admin actions to their own controller.

Eventually this should use standard RESTful routing.
Move incoming message admin to its own controller.

Make specs that depend on multiple controllers and models interacting
integration specs.
Slightly nicer action names.
Make prominence states a constant so we can access them elsewhere.
Add incoming message update action and route.

We'll use this for saving the changes to the prominence of an incoming
message in a relatively RESTful url structure.
Shorter route names and paths