mdDialog: button sizing does not match specification

[ThomasBurleson]

Buttons have side-padding of 8dp and 64dp min-width. See "Dialog button container" (even though the name, the specs applies to flat and raised buttons)

@see http://www.google.com/design/spec/components/buttons.html#buttons-usage

[marcysutton]

There are conflicting specs for dialog buttons. The dialog component spec shows 8px to the right of a button, not 16px:

Cards also show 8px. http://www.google.com/design/spec/components/cards.html#cards-actions

Our demos conform to this–the only change I can see is needed is side-by-side buttons should be separated by 8 pixels, not 4.