Lets add some ui

Known issues:
- The way I'm redirecting from index to search is hella-ghetto. What's the proper Rails way to do this?
- Image size is wrong on the welcome index page. We need a migration to fix this, will do that in a separate PR.
- v1 UI. Still lots of little things I could do to make it prettier, still lots of room to add features, still time to overhaul this if everyone hates it.

Here's how this looks now:
![welcome](https://cloud.githubusercontent.com/assets/590055/3781467/8b27c5a6-1996-11e4-8ee0-27bd6ff7f0ff.png)
![search](https://cloud.githubusercontent.com/assets/590055/3781468/8b28246a-1996-11e4-89b0-0f059b54b2f1.png)
Yeah, I waffled about moving back to a <form>. It felt unnecessary, and it would be a little messy to set the selected friends properly, but it's definitely better than my messy AJAX hack.