[refactor proposal] Separate existing and draft media

[denyskon]

The useMediaFiles hook and other media management code is a mess, especially because the behaviour is very different between the media library tab and the draft entry editor. To make it easier to maintain, I propose to separate 'media files' which already exist in a folder and are being retrieved from the backend, and 'media operations', which contain file replacement, creation and deletion. This would consist of the following changes:

• add mediaOperations to Entry interface
• simplify useMediaFiles to a unified method
• implement a method to put mediaFiles and mediaOperations together
• refactor creation, deletion and replacement behaviour -> possibility: implement "draft deleting" inside entries, batch media operations

I would try to implement this refactor, but first I want to know what you think about it @KaneFreeman

[KaneFreeman]

That sounds like a good approach to me.