:sparkles: Add option to upload background image

[diveresque]

Using react-dropzone and FileReader to allow user to upload image from computer onto background-image of the banner #5

[diveresque]

Hi @christopherkade have done the basics for upload images, needs a bit of tweaking, but thought its good to get some feedback at this point.

Also the checks didnt work as you can see - the error says to run yarn add react-dropzone, is that correct?

[christopherkade]

This is awesome work, I've been fiddling around with it and you did a great job.
Make sure to remove package-lock.json, we already have a yarn.lock 😄

I've done a code review, most of these changes are tiny so don't worry if you see so many comments !

[diveresque]

Thanks for the feedback, I am going through these. Im happy about the many comments, its good to learn! :D