nearly finished with nessus csv report support

- added Services() class to start fleshing out db abstraction a bit
- menu modified to remove XML-specific
- renamed import_xml_scan to import_scan
- much parsing, so loopy
CVSS fixes primarily
vulncloud and xml import fix
Severity fixes
lazy_tables setting in yaml sample
CVSS vector fix when CVSS2# not presented
Fix for n/a dates and csv maxsize
Merge pull request #66 from grutz/nessus_csv

Nessus CSV support and fixes!