Enhancement: Allow setting view mode for apps via query

We've added a new query param 'view_mode' to the app URL to allow setting the view mode for apps.
If the specific app and permission allows it, the view mode can be set to 'view' or 'write' via the query param.

https://github.com/owncloud/web/pull/11668
https://github.com/owncloud/web/issues/11667
