apply indicator element on multiple websites

[jossef]

Support the registry websites such as npmjs and pypi.org. These sites need a custom UI component because we want to add this component as a static part of the page.

generic code to modify the content of selected websites (not *) to load and add the indicator element tag e.g.

• [x] npmjs.com (#74)
• [x] pypi.org (#75)
• [ ] reddit
• [ ] github issues comments
• [ ] twitter
• [ ] #86