[UPDATE] Allow deletion of accounts

    Updated backend and theme to be able to deal with deleted accounts

    * Backends will skip any users that have no account_id associated with
      their shares
    * Updated round stats theme to show users as unknown if none can be found

    This will not fully address the issue of account deletion but at least
    wont break the system anymore.
Merge pull request #1312 from TheSerapher/issue-1061-deleteuser

    [UPDATE] Allow deletion of accounts