Home Page: update template to match current design

[pdpinch]

acceptance criteria:

• match current design, including template & styles
• header consistent with the rest of the site (implement new header design for the home page #730)
• Pull Program thumbnails, descriptions and links from program model (see also Home: What to do with very long program descriptions #653/Home: add character limit to program.description in django admin #658, Program page boxes on home page show link cursor even when there is no link to click #573)
• fix CSS issue (Fix home and program page styling on dev instance #892)
• update styling of mail form to match new design
• fix https bug in mail form Home: mailchimp signup needs to use https #965

related issues:

• CMS: update program thumbnails, description and link #944 allow updates to program thumbnails, etc.
• Home: Sign Up / Get started modal #917 Sign Up / Get started modal