UI: Automate displaying post-early voting content

It's been brought to my attention that several people will show up to an early voting location on election day. If you want to vote on election day, you need to go to your regular polling place, not any early voting one.

Ticket #49 outlines two new pieces of content:
1. To be displayed after early voting but before/on election day
2. To be displayed after one election but before early voting is approaching for the next election

Ideally, this change in display would be automated using the existing Angular app. We already have the election dates included in the app, so if it's currently within a given date range, we can have the site display different content.

Combines with #49 and #50 as a feature

Start by reading the existing Angular app's election-date handling and the content described in tickets #49 and #50. The work is done when the site automatically displays the appropriate content for the period after early voting, election day, and the interval before the next election's early voting.

Written by the indexing model from the issue text.