[selectors-api] Support Selectors API Level 1

(DocumentImp::querySelector, DocumentImp::querySelectorAll, ElementImp::querySelector, ElementImp::querySelectorAll): Add more details
(CSSParser::parseSelectorsGroup, CSSParser::getSelectorsGroup, CSSParser::setSelectorsGroup): New
(CSSSelectorsGroup::evaluate): New
(CSSPseudoClassSelector::match): Refine
(CSSTokenizer::getToken): Support StartSelectorsGroup
idl/selectors.idl: Update to W3C Proposed Recommendation 13 December 2012
src/css/CSSGrammar.yy (dom_selectors_group, START_SELECTORS_GROUP): New