T27464 CEST generic readers.

Summary:
Improved QmitkFileReaderOptionsDialog to only show the options box if a reader with options is selected.

Introduce BaseDicomMimeType and CEST DICOM manual mime types

• BaseDicomMimeType removes redundancy in code logic for mimetypes work with DICOM image files.
• Introduced special mime types that indicate that we have DICOM images with and w/o an CEST_META.json specified in the same directory.

Introduced public methods to extract CEST offsets and CESt T1 times.

Added consitency check (time steps count must equal offset/trec count) to CESTGenericDICOMReaderService.

Test Plan: review and application test

Reviewers: O3 MITK Reviewer Group II, O1 MITK Reviewer Group I, kislinsk

Reviewed By: O3 MITK Reviewer Group II, O1 MITK Reviewer Group I, kislinsk

Subscribers: kalali, kislinsk

Differential Revision: https://phabricator.mitk.org/D321