Implement Image Upload -- api/card/image

[waltervan00]

Images of the business cards can be uploaded for each card stored. This functionality needs to be researched.
It has been decided that the backend will enforce a size limit of 1MB, and that the front end is to offer resizing capabilities for this purpose. Atlas cluster has 512MB size limit. This endpoint acts independently from card CRUD operations.

http://expressjs.com/en/4x/api.html#res.send outlines how files can be sent back to the client.
https://www.npmjs.com/package/mime library offers MIME support for node.

• Research how images can be stored on the database
• Decide on whether to allow size limit, compress, or use GridFS
• Edit schema to fit needs.
• Defining API in documentation

• implement endpoint in back end for POST
• implement endpoint in back end for GET