Moves shell below key features

[rgommers]

This is a rebase of gh-221, to clean up the git history. It adds one simple commit to reduce the minimum height of the news bar (as suggested in #221 (comment)).

The only things left from gh-221 are:

• Create a news.md page (I'll create that next), and make the news bar link to it.
• The suggestions from @InessaPawson about making the colors of the dark areas on the front page more uniform (Moves shell below key features #221 (comment))

[rgommers]

Everyone seemed happy with this on gh-221, so merging. Thanks @joelachance and @InessaPawson !