Summary:
Now all elements by default have selection set to inherit with the root
level body object set to no selection.
This makes everything (except input elements) not selectable by default.
You can explicitly set the css class or use the new `.selectable` class.
Test Plan: edgehill --test
Reviewers: bengotow
Reviewed By: bengotow
Differential Revision: https://review.inboxapp.com/D1355