DICOM SRO exported transform inverted

[cpinter]

trafficstars

When testing the SRO export, it turned out that when we export a transform to SRO then import it, then the imported transform is the inverse of what we exported. This is inconsistent, and needs to be addressed.

Things to consider:

• Plastimatch inverts the transport at the time of export
• Slicer cannot blindly invert a transform when importing, because it may not have been exported using Plastimatch

@lassoan @gregsharp