Changed /drupal.org into /www.drupal.org.

Somehow d.o now has __www.__ prefixed. Dreditor breaks with 

> XMLHttpRequest cannot load https://drupal.org/node/1120672. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://www.drupal.org/' is therefore not allowed access.

That is for my #93 

This PR only changes other files.
The project issue link input filter is only enabled on the drupal.org main site and only works for issue nodes located on that site.  Links to groups.d.o, security.d.o, etc are not valid candidates.

Let's prefix the hard-coded domain name with an optional subdomain; i.e.,
```
(?:www\.)?drupal.org
```