(core) Refactoring google drive plugin

Summary:
Finishing implementation for google drive plugin.
- Refactoring plugin code to make it more robust and to follow grist ux
- Changing the way server hosts untrusted user content, from different domain to different port

Test Plan: Browser tests

Reviewers: dsagal, paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2881

app/server/mergedServerMain.ts

@@ -128,6 +128,10 @@ export async function main(port: number, serverTypes: ServerType[],
     await server.addDoc();
   }
 
+  if (includeHome) {
+    server.addClientSecrets();
+  }
+
   server.finalize();
 
   server.summary();