Update identity manual.
    
    - Previously, the book title was "The CentOS Artwork Repository
      User's Guide." This update changes the book title to "The CentOS
      Project Identity Manual."
    
    - Previously, there was not book preface. This update adds a book
      preface with an introduction to corporate identity. It also adds the
      copyright and feedback sections.
    
    - Previously, there was not licenses included in the book. This update
      adds both GFDL and GPL licenses at the end of the book, grouped in a
      part named Licenses.
    
    - The part of the book related to CentOS identity was revised and
      improved.
    
    - The repository mission was revised and improved. It reflects the
      fact that the CentOS artwork repository is a community effort
      focused on organizing and automating the production of CentOS
      identity.