Gulp esm

[roblarsen]

closing #2824 which forces us to do something useful. Since ES modules are supported natively, we can get rid of babel and still use modern JS.

This PR:

• removes babel as a dependency
• changes the gulpfile and the two test scripts to be .mjs All three were already using import, etc. so the upgrade was actually pretty easy. The specific change was to fix all three scripts to be able to read json files
• updates the eslintrc file to recognize the ability to do the above

[roblarsen]

@coliff this is good to go, I think.