Remove report-a-problem from 4XX pages

We shouldn't make users fill this out:

- this form captures info that we already know (from fastly or GA)
- this feedback isn't really being used in a consequent manner

This has been agreed with Roo.
Merge pull request #421 from alphagov/remove-report-a-problem-from-4XX-pages

Remove report-a-problem from 4XX pages
Don't ask Chrome 34 users to upgrade

We still get a lot of usage for it, and it's not _that_ old. Err on the side of not annoying users
Increase the browser upgrade dismissal duration

As some users are not in a position to upgrade, eg, anywhere with restrictive IT policies and slow update rollout.

While we still want to re-remind users, we shouldn't do it too often. A month seems reasonable
Update 404 page content

- New title and body links.
- Adjust test for output.
Merge pull request #422 from alphagov/update-404

Update 404 page content
Merge pull request #423 from alphagov/browser-upgrade-behaviour-tweak

Make legacy browsing checking less aggressive