Integrate Collabora OfficeServer implementation

Since the version of the Collabora Connector 1.6.0, we have the possibility to replace XWiki's default office server with an implementation that uses Collabora as an office server to convert documents.

This is a nice feature, as currently we don't ship a LibreOffice server in the XWiki container used by openDesk, for compliance reasons. This feature would bring the possibility to have a true office document import / export in openDesk.