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>
If this is modified(?) copy of some Eclipse/WTP class we should not use the standard JBoss copyright. Please see examples of such modified classes in any xpl packages.