[WIP] EZP-23748: As an editor, I want to be able to fill the image field

JIRA: https://jira.ez.no/browse/EZP-23748

# Description

<img src="https://raw.githubusercontent.com/patrickallaert/patrickallaert.github.io/master/assets/travaux4.gif" alt="WIP">

## Tasks

* [x] Implement a basic Image field edit view
* [x] Avoid sending the image content even if it was not changed
* [ ] Improve the CSS to better handle small images (width < 300px)
* [ ] ~~Drag an drop~~ (will be done later in https://jira.ez.no/browse/EZP-23789)