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.

I disagree, if they are there and not being used they become bloat. Because they are a core part of HTML doesn't mean we need to style them.

When I have used `blockquote` I end up just deleting these and starting from scratch anyway. Have you used these styles or close to them in a design?