feature(switch): background color is configurable
refactor(buttons): more control and customization

Changes:
- rename .buttons-row to .segmented-control
- add _segmented-control.scss partial
- add .button-small, .button-large, .button-primary, .button-block, and
more classes
fix(buttons): various sass fixes, expand button hit area
fix(segmented-control): adds import() to main file
refactor(range-slider): more customization, akin to UIKit

- variable naming conventions try to be familiar to UIKit developers
and Sass developers
feature(build): add Sass source map support
refactor(switch): move to its own partial

- also various button fixes
fix(buttons): prevent :active opacity change

Affects buttons with .button-outline or .button-clear
refactor(sass): move control partials into subdirectory

Affects the buttons, segmented-control, slider, and switch partials
fix(switch): change outline width to 1px
fix(slider): change customization possibilities

Remove the track-height variable, too finicky. Add thumb box-shadow and
border variables.
refactor(button): rename _buttons.scss to _button.scss
feature(sass): add horizontal rule styling
fix(button): improve resemblance to iOS7
feature(button): add disabled styles

Affects buttons that have .button-outline class when :disabled or
.disabled
feature(stepper): add stepper control
fix(stepper): vertically center text
feature(action-sheet): add action-sheet module

- .actions-modal is now .action-sheet
- submodules are now more semantic (e.g. using button elements instead
of spans)
- limitless customization
feature(build): add size output
fix(sass): remove ionicons

Speeds up build time more than 2x