Enforce a maximum length when setting the implementation version

[will2hew]

In the DICOM spec, the implementation version (as set by the setImplementationVersion) should be a maximum of 16 characters.

We observed in the wild silent failures - association requested, association accepted, and then abandoning the connection - no discernible error on either the DICOM SCU or on our SCP.

I would recommend we enforce that in dcmjs-dimse to prevent such a tricky error causing someone else pain in the future!