Closes #41.  Changes are:
* implemented CP-ITI-731 -- new DICOM schema for Audit Trail
* implemented CP-ITI-493 -- audit successfully delivered and failed documents in different audit records
* drop checking completeness uf audit datasets, deprecated URL option 'allowIncompleteAudit'
* implemented 'PurposeOfUse' option of ITI-20 (ATNA Audit) and ITI-40 (XUA)
* use OpenSAML for parsing XUA SAML2 assertions
* MockedSender performs XML validation of incoming audit records
* verison of OHT ATNA framework upgraded to 2.0.0-p3
* fixed home comminity ID codes in audit records of ITI-18, 38, 63
* dropped support for AbstractAuditInterceptor.XUA_USERNAME_CONTEXT_KEY in favor of AbstractAuditInterceptor.XUA_SAML_ASSERTION