[FEATURE] Validate file types.

[rosiel]

Overview of feature request

We've had the experience of uploading files that were not the type their extension claimed they were.

1. Install the File Mime Validator module https://www.drupal.org/project/file_mime_validator
2. Provide a hook so we can validate incoming derivatives too, since the validator only works on the upload widget.

What kind of user is the feature intended for?

Repository managers
Admins

What inspired the request?

reading the PREMIS Data Dictionary.

What existing behavior do you want changed?

We don't validate files!

Any brand new behavior do you want to add to Islandora?

Validate all files!

Any related open or closed issues to this feature request?

not that i can find