ZEVA 2: Attachment/dropzone modifications

**Describe the task**
currently when attachments are added to vehicles, when you select one file and then click to add another file it replaces it. Since multiple files are allowed could we make this more user friendly and just add files to the array rather than replace?

Also, if you are editing a form and resave it, it adds the new attachment to the vehicle file attachment table but doesn't erase the old one, should we replace or archive older files in the db?

Finally, we are currently not displaying attachments at all on the vehicle details page or form, maybe we should display at least the filename (and image??) so the user can see theres an attachment