Summary: When clicking a node in the tree, currently it expands or collapses the subtree under it. This adds a chevron button which only handles the expansion functionality, and clicking on the label with the Section name will show info about that Section in the side panel.
Reviewed By: fabiomassimo
Differential Revision: D17165150
fbshipit-source-id: ac6b6c127b68274f53523b3ea62422ff96116e9b
d77b5f0062