Support platform-wide alerts

[nickoneill]

There are certain times when we want to display important information to every user, for example during new sessions of Congress, the information behind the new reps is not always updated immediately after swearing in. We need to be able to display a message to users that they might see incorrect reps and we're working on getting things updated.

We should do this work before the 119th Congress starts.

• Consume the endpoint at tbd on startup, refresh at least every 24h
• Display a message on the dashboard, you can remove extraneous views (ex: newsletter signup) while this message is displayed