Normalize text of ParticipantObjectQuery in DICOM audit parser

[qligier]

In DICOM audit messages, ParticipantObjectQuery is a xsd:base64Binary, which collapses whitespaces. When reading it, we should normalize the value before trying to base64-decode it.

Currently, it fails if the XML is indented:

<ParticipantObjectQuery>
    VVRGLTg=
</ParticipantObjectQuery>

We can use getChildTextTrim instead of getChildTextNormalize, because whitespaces are not allowed inside the base64 content, so there's no point in normalizing them.

[unixoid]

Thank you @qligier !