Add nginx route to handle 502 errors from killed unicorns.

As opposed to a non-existant unicorn. We use some care to keep
a redirect loop from happening.

This is intended to handle requests that are uploading large files
and take too long. Typically Fedora takes a while to ingest files,
and if it takes more than 60s the unicorn master kills process handling
the request. This configuration will catch that error and give the user
a nicer error message.
Merge pull request #120 from ndlib/nginx_502_redirect

Add nginx route to handle 502 errors from killed unicorns.
adding page for timeout error to be used by ngnix

creating help request form and submit it as part of 502

Reverting changes in static page controller and issue post request directly to help_request controller

Adding static pages action for 502

Instead of a true static page, the /502(.html) route is sent to the
StaticPages#timeout_error. This allows for the generation of a
form with the CSRF token.

Resolves ndlib/curate#29 without a need to merge this pull request.

@TODO - This means that the HelpRequest model needs adjustment within
the local instance of CurateND. The 502 error may not have a current
user. Which means we need a fallback email to be the sender of the
help request.

Let user to create help_request on timeout with curate help email when sender email is not available
Minor UI change on error  page

[skip ci]
Merge pull request #121 from ndlib/502_error_page

adding page for timeout error to be used by ngnix
Bumping Curate version

$ bundle
Updating show view for consistency