Format with Prettier

It would be great if edited files were formatted with Prettier (https://prettier.io/) on save, if prettier config is found in the project folder.

Otherwise, the formatting is all thrown off and different each time the file is saved in VS Code/IntelliJ vs. Pinegrow.

Prettier can be invoked either by CLI command or JS API, either way, it shouldn’t take more than a few lines of code.

Thank you.