Change UX and design and whatever

* I'm sick of good commits, I'm sorry
* Add bourbon and bitters
* Messed with styling
* Played around with links, buttons, headers
* It has not-heinous UX and styling for the most part now
Yeah. So like, if you're looking at apartments on craigslist and you click on one, you probably want to then go back to the apartments, right? So I thought it was important to have this button. But since posts can have multiple categories, you can't just have a button to the category show page or that mentions a path w/ category id. So I used :back instead. But if you got to the post via a link on facebook or by making a new post, then that button is going to send you back to facebook or the form, which is totally bizarre. So this makes the button only appear if you arrived at this page via a url that included categories. It's not beautiful but I couldn't find a better way.