Remove button element scoping to lessen selector specificity

The less specific selectors are, the easier they are for people to override
with custom values.
Remove single use  variable
Rename variables as specified in TODO
Move all variables to top level import sheet

Some of the variables were being re-used between the two sheets; pulled them
up so they can be shared.
Remove single use mixins

Until these rules need to be used more than once, removing the mixin and adding
directly to their elements allows for better readability.

Also removed some style and selector duplication, old notes, and stray
whitespace.
Move gradient mixin to utilities partial
Standardize IE scoping style rule pattern

Anywhere we're scoping a style for ie, do it with an &/parent selector.
Move themed styles into a theme partial

This will let us build easily with two different "browser" stylesheets.
Move the remaining button styles into calculator partial, delete math_buttons

The distincton between button and calc layout was always fuzzy, but we can make
the distinction between layout and theme distinct.
Order properties, remove in-property and inhereted duplicates
rm styles on the calculator class, in prep for reducing element complexity
Simplifications for IE8 compatability code
Remove apangea styles (and consequently all !importants :D)
Revise the calculator style sheets to output a structure file and a theme file
Clean up theme vs structure css
Remove apangea cruft
Scope all CSS classes with a  module name, remove apangea dead code
Add steps to build process for new file, build dist, bump bower version
Merge pull request #10 from thinkthroughmath/rw/less-specificity

Sass/CSS optimizations