Add content/button to main view at the bottom of the airport list

[lynnandtonic]

Because not all airports will be included now (and possibly forever), when the user scrolls to the bottom of the list, let's add some content and a call-to-action. Something like:

Don't see your airport here? Find out more.

• add content and button
• button links to About page

Maybe we could do a contact form in a later release.