JBIDE-17849 CSS Hyperlinks aren't working on non-WTP projects

CSS Files path resolution is fixed, CSS Hyperlink, Create New File Hyperlink are fixed
JUnit test is added in order to test CSS Stylesheets inclusion using absolute and relative URLs

Signed-off-by: vrubezhny <vrubezhny@exadel.com>
Yes, it's modified a bit, but probably you're right. The most of the class is a copy of URLModelProvider. The only one method (resolveURI()) is modified (it cannot be just overridden because it's static). So, I'll put the comment from the original class here.