Template path was hardcoded

Symphony allows for changing the template path via the `PAGES` constant, but the path was still hardcoded for XSL imports.

I was wondering why this is implemented as an empty template importing the actual template instead of using the actual template directly, so here's a little background...

First XSL import is always relative to the executing script. In our case this is `index.php`, so our imports would be relative to the `DOCROOT`. Importing the page template itself changes the context for further imports, so we can import relative to the page template instead of the `DOCROOT` in our templates.