Notify user if file is bigger than upload_max_filesize

[jfauske]

If a user try to upload an image bigger than upload_max_filesize we get an error from Cloudinary, the xhr request returns a 500 and the UI become unresponsive to the user:
[2019-10-09 10:31:57] request.CRITICAL: Uncaught PHP Exception Cloudinary\Error: "Nothing to load" at vendor/cloudinary/cloudinary_php/src/Uploader.php line 514 {"exception":"[object] (Cloudinary\\Error(code: 400): Nothing to load at vendor/cloudinary/cloudinary_php/src/Uploader.php:514)"} []

Let the user know that the file they are trying to upoad is too big and can not be processed.

Version 1.0.13-aplha