feat(PDF):Add PDF viewer (#2730)

Display DICOM encapsulated PDF documents in a PDF viewer.
Addressed the remaining PR comments, and am merging this.

extensions/dicom-pdf/src/id.js

@@ -0,0 +1,8 @@
+const Name = 'dicom-pdf';
+const id = `org.ohif.${Name}`;
+
+export default id;
+
+const SOPClassHandlerId = `${id}.sopClassHandlerModule.${Name}`;
+
+export { Name, SOPClassHandlerId, };