Allow package manager to resolve voice intent

Also made the activity translucent so that it won't flicker when the user pressses the button and Google app is disabled

* Replace strings, add learn more, hook up button

* Constrain learn more and icon to the text

* View holder tests

* Lint

* Update homescreen ui test

After the change from AC #8054 specifying different addons icons backgrounds
is not possible anymore.
All favicons used all throughout the app will have the same background.

* Add notifications pref in top level settings to route to Android app and notification settings

* Make pref visible on Oreo and higher

* Only show notifications pref when Oreo and above

13899 re worded the performance readme and removed the reference to debuggable builds

13899 fixed some nits

As Google's library for showing licences isn't open-source, this commit
reimplements its main Activity. This is in prevision to having an OSS
flavor of fenix.

We chose to not introduce dependencies to third-party libraries
such as AboutLibraries for now, and we'll stick to using Google's gradle
plugin for the dependencies extraction.

Fixes #7584

See also #162

Also removed it before reference is removed in onDestroy.