chore(grunt): add jscs task to test task

It is too easy to forget to check jscs for things like trailing whitespace
before pushing commits, such as simple doc changes.  This then breaks the
build and is messy.  Adding jscs to the test task gives people a slightly
better chance of catching these before pushing.
docs(css): ensure all type-hints have a background color

If the type of a type-hint was not recognized, say a "Promise", then
the background color was left as white.  Given that the default
foreground color is also white, this meant that such type-hints were
invisible.

Closes #6934