Make a function for parsing help query param

Our templates are a littered with `request.args.get('help', '0')`.
This commit refactors these into a single helper method, which can be
used by the view functions, then passed to the template.

This makes the templates cleaner, and should make it easier to refactor
`help` out of the query parameters entirely in the future.

app/templates/partials/jobs/notifications.html

@@ -4,7 +4,7 @@
   <div class="dashboard-table">
 {% endif %}
 
-  {% if notifications and request.args.get('help', '0') == '0' %}
+  {% if notifications and not help %}
     <p class="bottom-gutter">
       <a href="{{ url_for('.view_job_csv', service_id=current_service.id, job_id=job.id, status=status) }}" download="download" class="heading-small">Download as a CSV file</a>
       &emsp;