Clean up HTML and CSS for feed card buttons

When the buttons fade out, the "Edit" link no longer hangs around for
too long, I also fixed it to look like a proper button.

I began to do some proper CSS class-prefixing, e.g., ".feedcard
.btn-container" rather than allowing .btn-container to be a top-level.

Also did some quick cleanup to put each CSS selector on its own line.
This way, it's much easier at-a-glance to see that ".class1, .class2"
actually refers to two separate selectors and not  ".class1  .class2".
Style editor, hook up jQuery Tags Input plugin

I moved reset.css into its own file, and re-ordered the CSS imports so
the cascade can work properly (reset, bootstrap, flat-ui, our CSS).
Simplify header component and fix its misbehaving styles

Our bespoke header CSS was conflicting with the flat-ui styles, so now
we override them in a few ways. Nav buttons are now flush with the
bottom of the nav bar!
Use :hover to simplify feed card mouseenter / mouseleave tracking
Fix up reviewing top and left coordinates

Looks like they got reversed.