unified 'npm start' for both desktop and web

Using updated office-addin-debugging package which allows
reading values from npm config/scripts in package.json.

It also supports an appType optional argument which can be added so
that "npm start web" will do the appropriate thing and the user can
manual upload the manifest into an Excel Online document.

"npm start" defaults to desktop. This can be changed in the
package.json config "app-type-to-debug".

Author: akrantz

.vscode/tasks.json

@@ -31,7 +31,7 @@
         {
             "label": "Debug: Desktop",
             "type": "npm",
-            "script": "start-desktop",
+            "script": "start",
             "presentation": {
                 "clear": true,
                 "panel": "shared",