Implement new integration with CRash

The goal is to improve over the existing integration at http://extensions.xwiki.org/xwiki/bin/view/Extension/CRaSH+Console with:

• Use a new version of CRaSH
• Use a different way to integrate it (as suggested by its creator Julien Viet)
• Focus initially on just providing a SSH access to the CRaSH console
• Allow adding new CRaSH commands in wiki pages