[mediaqueries] overflow-block/inline

While I'm sympathetic to the differences between block and inline overflow,
and it may indeed be necessary sometimes to query them independently,
I think it's probably easier for authors if we provide a simple 'overflow'
query:

overflow: none | scroll | scroll-page | page

where the author assumption is that if it's 'page', then there's no
inline scrolling, although the UA may allow it.

Also, I suggest the following renamings:
  paged -> page for grammatic consistency with scroll
  optional-paged -> scroll-page because it does both, it's not just paging

~fantasai