test(throttle): fix some broken tests
test(throttle): temporarily disable some broken tests
docs(): Make menu-items accessible buttons

Closes #132. Closes #133.
fix(material-toolbar): Update to use headings

Closes #130
fix(material-toolbar): Add support for link

Closes #130
fix($throttle) - logic scan for throttle function no longer uses `=== null`
demo(material-toolbar): use new flex attributes

Addresses #130
demo(tabs) - disable text transform for testimonial demos
refactor(checkbox): remove nested `<input>`

Closes #121

Don't use nested `<input>`:
* simplifies the usage of checkboxes
* we already render the buttons ourselves with canvas
* polymer radio component also does not use an <input> internally

Don't create scopes for the buttons
* helps preventing newbie problems with `ng-model`

Reuse original `inputDirective`
* saves code while preserving features (E.g. ng-true-value`)
* only a little bit hacky but works nice
refactor(radio): remove nested `<input>`, put `ng-model` to group

Closes #121

Don't use nested `<input>`. This is ok as:
* simplifies the usage of radio buttons
* we already render the buttons ourselves with canvas
* polymer radio component also does not use an <input> internally

Place `ng-model` on `<material-radio-group>`
* simplifies the usage of radio buttons
* before it needed to be repeated on every radio button

Don't create scopes for the buttons
* helps preventing newbie problems with `ng-model`
docs(): promote LAYOUT, remove UTILITIES

Closes #129
fix(material-sidenav): properly add backdrop
fix(sidenav): use a backdrop element
refactor(): remove popup service, remove backdrop service. simplify.
test($materialToast): fix tests
docs(): separate demos and api documentation
docs(): s/COMPONENTS/API
docs(toast): fix closing html tag
docs(): add docs for sidenav
docs(): start rewrite of layout grid page