[Strings] Make description of NIUserInterfaceString useful.
[CSS] Fix performance issue where the ruleset order list could contain the same properties multiple times and become unreasonably long.
[CSS] Assorted performance improvements to [NIDOM refresh]. Also, adding a CSS class to a view no longer forces the DOM to refresh that view.
Merge pull request #29 from djMax/harder-performance-fixes

DOM refresh performance fixes