Merge ideas from nhnt11's template

[motin]

Let's merge ideas from nhnt11's template: https://github.com/nhnt11/WEE-Shield-Study-Template (created as a follow-up to the https://github.com/mozilla/blurts-addon study)

We can start with getting src simplified (and then look at how we best can set up testing in a simpler manner, but that is a separate issue)

[motin]

Whatever we do, we can start by simplifying https://github.com/mozilla/shield-studies-addon-utils/tree/develop/examples/small-study (see #48), and then updating the template to use the simplified boilerplate.

[nhnt11]

Thanks for filing this. I'll be looking into this this week.