handle case where required system properties are not set by informing user

Author: rs-fraser

src/main/webapp/scripts/externalTinymcePlugins/googledrive/plugin.min.js

@@ -8,6 +8,10 @@ via scripts imported in `header.jsp`.
 let accessToken;
 
 async function insertFromGoogleDrive() {
+	if(!gdClientId || !gdScope){
+		apprise("Missing required system properties for google drive "
+				+ "integration. Please speak to your rspace administrator");
+	}
 	await gapi.load('client:picker');
 
 	const client = await google.accounts.oauth2.initTokenClient({