User.LoadFile: Load user files
==============================

Implement this method:

.. function:: LoadFile(filename string) (data []byte, err error)

    If the file does not exist, return an error.

    If the file exists, download the latest version of the file. If loading the
    file cannot complete due to some malicious action, return an error.

    Verify the integrity of the downloaded file. If there have been any
    unauthorized modifications to the file, then return an error.
    
    If the file could be downloaded and its integrity was verified, then return
    the contents of the file.

    :param filename: File name
    :type filename: string
    :param data: File contents
    :type data: []byte

    :rtype: []byte, error

.. warning::
    Do not forget that your design must satisfy **all** requirements, including:
    
    #. Users can have multiple active user sessions at once (see
       :ref:`requirement_user_sessions`).