First step towards single tokenization.

First step towards single tokenization.

* Removes tokenization from all steps in favour to single at the beginning.
* Adds tokenization of properties value by value instead of all in one piece, e.g.
  `margin:0px 1px` gets tokenized into `margin`, `0px, and `1px`.
* Full tokenization means more detailed source maps too.
* Reworks override compactor and associated classes to use single tokenization.
* Simplifies override compactor code so it's much easier to understand.
* Adds loads of tests to override compactor and family.

Caveats / in progress:
* Shorthand compactor is turned off.
* Inherit compacting is gone (but will be back).
* Some multivalue background tests are failing.
* There's no way to turn off compacting (possible performance regression).