Add support for customising configuration

[matdehaast]

Thanks for this great tool!

Would be great to add support for customising the configuration object

[renanlecaro]

@matdehaast this would be quite easy to do as we just need to add another key to the json we store in alt text. However, i'm not sure of how to get this to look good ui wise, a json blob editor is not really user friendly. Feel free to submit a pr.

[renanlecaro]

@matdehaast except the theme, is there anything that should be configurable ? I'd like to close this issue unless there's something worth doing here