[CLEANUP] Refactor `parseCssRules`: parse all CSS (#528)
[CLEANUP] Refactor `parseCssRules`: parse all CSS (#528)

Refactored `parseCssRules` so that it can now parse an entire CSS string,
including @media rules.  It now returns two arrays, in an array with the
following keys:
- "inlineable" => The inlineable rules that would have been previously returned;
- "uninlineable" => The uninlineable rules, currently those from within @media
  rules.

The original line number information from the CSS is available in both arrays,
so the original ordering of all the rules (that will be required for #280) can
be determined.
MyIntervals/emogrifier,jjriv/emogrifier