fixes #314

fixes #310

Users may choose between filesystem (FS) or S3 to store and manage their media files

`episodes.manage-notifications` should be `manage-notifications`

Since CI4 v4.2.8, the actor route is not retrieved anymore, this prevents users from creating a
podcast.

remove validate_url custom validator and replace with CI4's valid_url_strict

--> Having a URL with spaces in the beginning or end would cause the platform to be deleted

set the right permissions for episode's publication date edit

fixes #249