Refactor npm scripts to have a clear install+test pattern

[mgol]

We should get to the point where npm run build installs & builds the project & npm test builds & tests it (including running linters) like in Core. In particular, that means running npm install && npm test (or it's alias npm it) is enough to run all checks for the current code that don't require spawning a real browser.

This idea originated in #155.

[mgol]

I have a problem with making the qunit task load a different Migrate in production & dev test mode. I need to have a way to pass GET parameters to test/index.html but that doesn't seem possible with the qunit task (at least unless we run a real dev server).