Feature: Support closing dialog windows (#233)

Supports closing dialogs in development. Upgrades gas-client to 1.2.0 and uses new API here: Add scriptHostFunctions for google.script.host gas-client#36
Example button to close dialog in Bootstrap sample
Updates integration tests

src/client/utils/serverFunctions.ts

@@ -1,10 +1,12 @@
 import { GASClient } from 'gas-client';
 import * as publicServerFunctions from '../../server';
 
-const { serverFunctions } = new GASClient<typeof publicServerFunctions>({
+const { serverFunctions, scriptHostFunctions } = new GASClient<
+  typeof publicServerFunctions
+>({
   // this is necessary for local development but will be ignored in production
   allowedDevelopmentDomains: (origin) =>
     /https:\/\/.*\.googleusercontent\.com$/.test(origin),
 });
 
-export { serverFunctions };
+export { serverFunctions, scriptHostFunctions };