Remove a bunch of redundancy in variables and header text styles

These changes are to  simplify bitters and are opinionated based on building web applications and not web sites.

* Remove header styles because they always get changed. The initial styles just add overhead to be changed. 
* Remove `blockquote` and `cite` styles. I've hardly ever used them and changed them when I have.
* Create `$base-spacing-small` for all the places where we were using `$base-spacing / 2`
* Remove unnecessary duplication in form variables.
* Remove unnecessary duplication in link and button variables.
* Remove `$base-background-color` as it rarely is used more than once.

Regularly. I usually consider `$base-accent-color` like a primary brand color, and `$base-link-color` something like what @whmii's describing as a "base-action-color"

[Here, for example](https://cloud.githubusercontent.com/assets/2317604/5376634/a21b2200-8046-11e4-8544-a7fc507467ba.png), $base-accent-color is for headers (and other stuff on mobile, etc), $base-link-color is for the button (and links on a subpage, etc)