Form: Updating Page: Rework infobox image

[Lenni009]

The infobox image is required for new bases, but isn't for existing bases.

We cannot input files into the file input like we can with other input types.

This means that if you don't upload a new file, it will be flagged as invalid.

-> There should be some form of visualisation of what you uploaded -> Take inspiration from https://www.nmswikiboilerplate.com/civ

The image property in the state should be replaced with a FileItem (or similar). This allows us to have a file or just a URL. The URL can also be used for the image element to show the uploaded image.