fix: broken grunt test

[Shashwat325]

grunt test was broken on modern Node.js with the following error:
Fatal error: The "cb" argument must be of type function. Received undefined

The dependencies on which the grunt test depends were outdated which led to this error. I fixed that by updating those dependencies via npm:
Upgraded grunt-contrib-qunit to latest version which now uses headless Chrome instead of abandoned phantomjs.

Added qunit as a devDependency in package.json.

Updated test HTML files to reference QUnit from node_modules so now the test will always use the npm managed version.

Added grunt-contrib-connect to serve files over HTTP for headless Chrome (required as Chrome cannot load files directly from filesystem like phantomjs).

Updated Gruntfile.js to use puppeteer with no-sandbox flags for headless Chrome compatibility

Fixed a pre-existing jshint scope error in examples/bigbrain-viewer-demo.js that was blocking grunt test from completing

Before

After

[Shashwat325]

@natacha-beck, any thoughts on this approach ?
I followed your suggestion from #370