Improve Foundation Meetings experience for Secretary

[glasnt]

As the DSF Secretary, I want to improve the experience for creating minutes of Board Meetings:

• Pre-populate Title/Slug "DSF Board monthly meeting"
• Add "is_active" feature, to allow for previewing of minutes (important once #1316 is merged, ensuring first-publication accuracy (like Blog Entries)
• Correct template showing empty elements where no Individual/Corporate members added that month (need to confirm data model around default empty listings -> empty entries)
• Add "content format" (like Blog Entries) to allow RST/HTML/None formatting.
• Make Board Attendees suggested list only include current board by default (multiple previous years pollute this list).

I'm happy to develop these features myself, but I can't assign myself this issue.

[glasnt]

• Pre-populate slug was fixed in https://github.com/django/djangoproject.com/pull/1387
• Content format is already in RST converted to HTML, I just default to using markdown which isn't RST so I was getting formatting issues.
• Correct template empty fields: PR fix in #1404
• Is_active feature: with the discovery about content format, I'm not as worried about this as much any more.
• Active terms: term is just a free text field, but by order of entry, the most recent are at the bottom of the list so that's useful to know.

I don't think I'll submit any more fixes after the current one.