Validate XML schema against xsd before loading, and die if not valid

Nother try. This validates the xml file's schema against the seccubus.xsd (located in /SeccubusV2/seccubus.xsd) and quits load_ivil if the schema is not valid. Made this because burp2ivil was giving me issues too and I had trouble finding out why. Issue also reported here: https://github.com/schubergphilis/Seccubus_v2/issues/103

Expects XML::SAX::ParserFactory and XML::Validator::Schema to be installed.

The in issue 103 supplied xml now fails nicely as thus:
![screenshot from 2014-05-20 16 32 54](https://cloud.githubusercontent.com/assets/1157977/3028655/df40ac72-e02d-11e3-8827-35a1d76057de.png)