enhance(ripple): improvements to API, sideNav list items, and button effects

add md-ripple-active support for nav active state,
add support for ms-ink-color to set a custom ink color, cleans up attribute names and re-arranges code,
rename method to be more consistent with our naming conventions,
add test for custom ripple ink color,
allow invalid entries for md-ink-ripple to be ignored,
change internal code for checkboxes and radio buttons to use md-ink-ripple-checkbox

Close #689.