Upgrade to cssparser 0.9.18

* Update: At some places the parser inserts synthetic universal selectors (*). Starting with this version a special class (SyntheticElementSelectorImpl) is used for these selectors. As a result, the output (toString, getCssText) no longer contains an extra '*' (if not explicit defined in the input)
* Fix: CSSStyleSheet.insertRule when taking the rule from an existing rule and the rule contains ':not'.
* Update: MediaQuery.isOnly() and MediaQuery.isNot() added.
* Update: MediaList.getMediaText now outputs the whole media query 
* Update: Colon is no longer part of the text output of empty properties.