Home page clean up

@laspluviosillas @davidclarkmoore  Here are a few tweaks to the home page. I didn't bother tweaking the images that are sized improperly because we haven't decided on the actual images that will go on the home page yet. @laspluviosillas I wasn't sure how you wanted to change the mission stories or which right arrows you were referring to in the "Share this!" text. Is it supposed to be a button?

@davidclarkmoore - I didn't see your previous branch by the same name (except with "Home" capitalized) so my apologies for any confusion. It appears your branch is pulled into the master so I'm guessing we can kill it. 
Also, @laspluviosillas  @davidclarkmoore have we three decided whether to have the side nav shift all the main content when clicking the hamburger, or just move the nav bar over? If it's the latter, I can axe the .shift class altogether along with the .side class and can remove the latter from the home.html.haml file.