The checks of DicomRTIOMimeTypes could be optimized to be more resource efficient.

1. DicomRTIOMimeTypes::GetModality(): We don't need to scan for all tags of interests, like we currently do. It is enough to just scan for the modality tag (DICOMTagPath(0x0008, 0x0060)). In addition that also removes the unnecessary dependency to the DicomTagsOfInterestService.

2. DicomRTIOMimeTypes::RTDoseMimeType::AppliesTo(): Should check first for the modality and only if it is the right modality, check its reader compliance. The later takes more time but is not that discriminating as the modality check and only a nice to have.