Improve the DicomDictionary so it allows multiple VRs per tag and specifies the tags VM

[Paolo Brandoli]

Currently the Dicom Dictionary defines only one VR per tag, but the DICOM standard allows for more tags.

Improve the dictionary so it allows more than one VR per tag.

Also, the dictionary should return the multiplicity (VM) for each tag (min value, max value, step).

[Paolo Brandoli]

Already implemented.