Bug fixes

fix the failure of the itkimage2segimage converter in the case when referenced instances list is empty

Improvements

DICOM segmentation context (coded terms describing the segmentation) has been updated to include the codes from the current version of the DICOM standard
DICOM parametric map diffusion and perfusion contexts (coded terms describing quantities/units used for encoding parametric maps derived by the quantitative analysis of DW, DCE and DSC MRI) have been updated, and now include terms included in the standard, and proposed for inclusion in the standard in CP-1665 (coding scheme 99DCMCP1665)
simplify initialization of DerivedPixelContrast: always use QUANTITY (DICOM CP not yet assigned a number!). As a result, the user is no longer required (or allowed) to specify this attribute in the metadata JSON.
minor fixes to the schema JSONs
more tests added
cleanup of CLI XML to improve consistency of the labels and fix semantics of the parameters
add dcmqi gitter channel - you can now chat with us on gitter (follow gitter badge in README)