Model page: Registry panel lists registry files, elements inside each

- one collapsible header per .archify-registry file with its element
  count and an Open button that opens the registry view; files start
  collapsed, the Registry panel open
- view types moved to views/viewTypes.ts so the diagram page can open a
  registry without a circular import
- 0.7.1

src/views/registryView.ts

@@ -7,10 +7,9 @@ import { readText } from '../util/files';
 import { log } from '../util/log';
 import { handleWebviewMessage, WebviewMessage } from '../webview/messages';
 import { makeNonce, registryPage } from '../webview/page';
-import { DIAGRAM_EDITOR_VIEW_TYPE } from './diagramView';
+import { DIAGRAM_EDITOR_VIEW_TYPE, REGISTRY_VIEW_TYPE } from './viewTypes';
 
-/** Default editor for .archify-registry files: the elements as cards, each with where it is used. */
-export const REGISTRY_VIEW_TYPE = 'archify.registry';
+export { REGISTRY_VIEW_TYPE };
 
 class RegistryDocument implements vscode.CustomDocument {
   constructor(readonly uri: vscode.Uri) {}