Add parsing and methods for metadata relevant for DICOM conversion

[erikogabrielsson]

• Allocated string lengths are based on the Length of Value for the VR that the corresponding DICOM attribute should have.
• DICOM_SOFTWARE_VERSIONS, DICOM_DATE_OF_LAST_CALIBRATION, and DICOM_TIME_OF_LAST_CALIBRATION are specified as IStringArray in the isyntax specifications, and could potentially contain multiple items.
• Although the corresponding DICOM attributes for DICOM_LOSSY_IMAGE_COMPRESSION_RATIO and DICOM_LOSSY_IMAGE_COMPRESSION_METHOD allow multiple values, the isyntax specification specifies them as IDouble and IString, so parse them as single values.

C is not my strongest language, so please review thoroughly and give feedback :)