Move global function CSS_URL() to static member function

Move global function CSS_URL() to static member function
of class Template (which is the only place it's ever
likely to be used.)

Also, minor fixes of code in that function:

 o Default CSS should be listed first (Galeon, at least seems to use
   order to determine which is the default.

 o Element attributes passed to Element() and QElement() shouldn't be
   htmlspecialchar()ed.  (Element() takes care of that.)

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@1172 96ab9672-09ca-45d6-a79d-3d69d39ca109