chore(docs): fix dartdoc indentation for application_factory
docs(Scope): explain `::` and `:` expression notation
chore(testing): upgrade guinness

Upgrade the Guinness library to fix the issue with `ddescribe` not working.

Closes #1029
chore(pubspec): Replace shadow_dom with web_components

The shadow_dom package is deprecated, see
https://code.google.com/p/dart/issues/detail?id=18080