Re-add extensions as top level dir

extensions/ohif-dicom-pdf-extension/src/OHIFDicomPDFExtension.js

@@ -0,0 +1,27 @@
+import OHIFDicomPDFViewport from './OHIFDicomPDFViewport.js';
+import OHIFDicomPDFSopClassHandler from './OHIFDicomPDFSopClassHandler.js';
+
+export default class OHIFDicomPDFExtension {
+  /**
+   * Extension ID is a unique id, might be used for namespacing extension specific redux actions/reducers (?)
+   */
+  getExtensionId() {
+    return 'pdf';
+  }
+
+  getViewportModule() {
+    return OHIFDicomPDFViewport;
+  }
+
+  getSopClassHandler() {
+    return OHIFDicomPDFSopClassHandler;
+  }
+
+  getPanelModule() {
+    return null;
+  }
+
+  getToolbarModule() {
+    return null;
+  }
+}