Summary:
Ref T13516. Deletes all old filetree / flex / active / collapse nav code in favor of the new code.
Restores the inline tips in the path tree.
Test Plan: {F7374175}
Maniphest Tasks: T13516
Differential Revision: https://secure.phabricator.com/D21154
Summary: Ref T13516. Apply basic UI styling to the new UI and make some more interaction work.
Test Plan: {F7374096}
Maniphest Tasks: T13516
Differential Revision: https://secure.phabricator.com/D21153