WS-Security for SoapServer + Apache Axis and SoapServer interoperabilty tests

New features/cleanups:
- [x] implemented WS Security for SoapServer (BeSimple/BeSimpleSoapServer#3)
- [x] extracted common code for WS Security handling to SoapCommon
- [x] converted existing interoperability test to PHPUnit and added tests for the new features of SoapServer
- [x] added bash scripts for travis to run the Axis and SoapServer interoperability tests

Fixes detected by adding the new tests:
- [x] fixed handling of SoapFault in SoapServer
- [x] fixed bug in Curl (function paramter was wrong)
- [x] fixed bug in SwaTypeConverter (missing cid: prefix required)
- [x] fixed bug in WsdlDownloader (vars must be always initialized)