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. 
an unspoken standard I personally manage is that if your CSS definition is one line just put it all in one line:

```css
a:hover { background-color: rgba(255,255,255,.1) }
```

Just to be clear, this is not a universal coding style, just a personal preference.