Reformat and add "new sheet to document" function

[JulesCastel]

I needed the ability to create a new sheet/tab to the document and couldn't find a way to do so, so I made my own way of doing it. I tested it on my own sheet and it seems to work fine, but further testing might be needed!

I also had a few nitpicks with the formatting of gsheet.js and gsheet.html, so I prettied them up as well to make it easier to read. There was also a typo with the word "flatten" (it was spelled as "flaten"), so I fixed that as well to prevent future headaches in case anybody else needs to work on it.

The new function is in the example flow in examples/Google Sheets.json too, to show how it should be used.

I'm new to contributing on GitHub btw, so please let me know if there's anything I might've missed here 🙏

[JulesCastel]

Forgot to mention, I also changed stuff in package.json when I was testing that I forgot to not include before I committed my changes whoops, that can be ignored lol