Partial #23 - Remove work arounds for Publican < 3.2

In particular:

* RHBZ#957956 - Book_Info.xml file is no longer required in spite of
                info_file directive.
* RHBZ#919474 - Case insensitive language attributes are now supported.
* RHBZ#953618 - UTF8 characters in image files are now handled
                correctly.
* RHBZ#919486 - All DocBook 4 conditionals are now supported.