Add Notice on display of Draft pages

[xmatthewx]

Currently, all Mezzanine authors can view pages with Draft status on the frontend as if the page was Published. This is great for a preview, but dangerous since many staff can assume a page is live and visible to the public when it is not.

Steps to Repeat:

• Create a new Opportunity Page via Mezz
• Save as draft
• Navigate to page
• Expected: page is visible as preview, with notice at top to Publish
• Actual: page is visible with no notice

Requirements

• The notice can be simple. Should display at top of all CMS editable pages that are not current Published.
• Yellow bar (#faf2cc) across the top with text that says:
  • "Draft preview. You must save as Published to make it public."
• Use notice component styles previously developed by Gavin
• A Page can be Published, but not live because of a future date or expiration date. We should show notice on ALL pages that are not visible. So, in pseudo code `if (status = draft || now != published ) { display_draft_notice = true }. We could get fancy with conditional notice copy, but that feels like extra complexity. Nice to have but probably not worth it.

cc @alanmoo to triage

[xmatthewx]

[alanmoo]

To implement this requires some extra Django/Mezzanine template code in opportunity.pug, which will get generated and added to landingpage.html.

I'm not sure what notice component styles you're referring to though. @gvn can you point them out?

[gvn]

I'm not sure either. We didn't do a custom alert style for Foundation AFAIK.

[xmatthewx]

I was thinking of the barn raising notice last spring. Yellow bar.

[alanmoo]

Looks like we need a wrapper

{% if not page.published %}
DANGER, WILL ROBINSON!
{% else %}