Update templates to include dates on all event pages

[mattstratton]

It is very useful for every page on devopsdays event pages to include the event date (not just the welcome page). Need to think about how to enable this with a good look and feel.

[adrianmoisey]

I agree with this idea.
It may take time to figure out how to add it to the template and make it look nice.

[bridgetkromhout]

@mattstratton and I discussed showing all existing event dates, even on archived events. Discussion in #8983.