Provide generic preview for File documents

There will always be some blobs for which no previews can be generated. UI should be graceful about this. Picture doc type already is.

Edit :

Currently, blobs with no preview leads to an error display (see attached screenshot-1.png) "{entity-type: exception, 404, no preview etc.}

On such case, a placeholder image should be displayed instead, similar to images for picture doc type when no file attached.

The illustration proposed is currently generic (see attached illustrations for v1 or v2).

In the long term (not scope of this ticket ?) a placeholder per doctype may be defined on the platform.