Update some functions and clean output results

Functions Updated:
convert_unix_timestamp - PEP8 formatting
get_report_hosts - return list of hosts instead of raw xml

Functions Added:
get_vulnerabilities
get_chapter_list
produce_xslt_report
get_xslt_report

Functions Deleted:
sort_data - not needed
produce_html_report - replaced by 'get_xslt_report'
get_report_pdf - replaced by 'get_xslt_report'