Additional minor updates to the docs

Minor fixes to docs

* Change .brand to .navbar-brand
* Change .btn-navbar to .navbar-toggle
* Redesign navbar toggle to be a bit lighter and wider
* Center align the navbar brand with a max-width of 200px (to minimize hit area) while still centering

Bring back the label, make it scale somewhat with the font-size of the parent using percentages and ems

* They're hidden by default in the mobile-first views because otherwise they just cover up the slides
* In mobile they're centered, and then are shown left aligned at larger viewports

* Drop custom type arrow controls for glyphicons icons instead for more consistent rendering
* Remove the captions and instead let folks implement what they want in the carousel
* Move the indicators to the bottom middle instead of top right
* Lighten up gradients on the edges for less harsh lighting