Update Babel and rename babel.config.js to babel.config.cjs

[aldeed]

The following is logged whenever Babel is involved (running tests mostly):

(node:39890) Warning: require() of ES modules is not supported.require() of babel.config.js from node_modules/@babel/core/lib/config/files/configuration.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which de
fines all .js files in that package scope as ES modules.Instead rename babel.config.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from package.json.

Babel 7.7.0 adds support for .cjs extension: https://github.com/babel/babel/blob/master/CHANGELOG.md#v770-2019-11-05

So the tasks:

• Update Babel and all related packages to 7.7.0, or as high as we can go without breaking things
• Rename babel.config.js -> babel.config.cjs to avoid this warning