New Feature XOVIS

This PR supersedes PR 126 and merges in the changes to xovis and the changes to the xsce structure.

N.B. That an existing xovis database is deleted.  And the delete step ignores errors in case the database does not exist.

N.B. That the admin password is admin and should be changed.

The variables have been placed in vars/default_vars.yml, where they should be overridden until we get a better home for them.