Add json syntax highlight

[gordonbondon]

Prism provides their own live syntax highlight functionality https://live.prismjs.com/ + https://github.com/PrismJS/live, so I decided to give it a try. Results look like this:

json-syntax.mov

Fixes #27

[flosell]

Hey @gordonbondon, good start!

One thing I noticed: There seems to be something odd going on with the PrismJS stuff and the underlying textbox. I can see the red spellcheck lines (I think that can be easily disabled) and when selecting I see the underlying text which looks very odd:

Screen.Recording.2021-11-02.at.07.56.02.mov

Also, two minor things:

• The input textbox looks quite small compared to the output textbox, probably needs a bit of styling
• The PR conflicts since I've merged your other PR