Builder v2: Files field: Add clear and Delete option

[Timo-Breumelhof]

In some cases you only want a user to be able to upload a unique document and the "old versions" should not be kept on the server.

Let's say we want a users motivation letter.

In that case you want to be able top add the letter, replace the letter an delete it from the server.

I suggest to add an option "replaceFile" which will delete the previous version when you upload a new one.
I do think a warning would be in place in this case (do you want to replace the document).
So that warning would also show when the filenames are not he same.
It would also have to delete the existing file if you clear the field.