Build: allow local demo to optionally run on transpiled dist code

[ianmcburnie]

So that we can catch and fix bugs in all browsers, we need to be running the transpiled dist code in our local demo.

Running yarn start should add a transpile step to it's pipeline, and local demo should have capability to be running on the transpiled code in dist.

Related to: #59

[yomed]

As discussed, the default case can be against src/, but there should be an easy way to run against dist/ for debugging edge cases. The prepublish and postpublish scripts take care of most of the dist setup, but we would also need to have a script that points demo to dist/. We could potentially make the publishing scripts more generic to achieve this.

[DylanPiercey]

After talking with @yomed I think an easier solution here would just be to conditionally add the lasso-babel-transform to the demo based on NODE_ENV.

We could then trigger the demo to start in dist/production mode by using NODE_ENV=production npm start and also probably have an alias like npm start:prod or similar.