Change title-handling and related things

The main feature was to remove the title validation and compute
something generic based on type and recipient. That was a relatively
easy and small patch visible as the migration and
SubmitNotice#generic_title.

That exposed a number of things:

1. The parameters have a different structure depending on if they came
   in from the web form or a direct JSON POST. See details in
   SubmitNotice#flatten_param

2. EntityNoticeRoles was, in some cases, saving nested Entities even
   when they were invalid. We never saw this bug until now because those
   scenarios were hidden by the Notice being invalid for other reasons
   (no Title).

3. Works had the same bug w.r.t Infringing/Copyrighted URLs.

4. The view didn't work as is ("<type> - <title>") since the requirement
   is that an empty title leads to "<type> notice for <recipient>".
   Changing this just meant updating the submit_typed_notice specs to
   rely on the generated title to verify that the right type was
   created.