Add collapse/expand functionality to company org chart page

This adds the ability to expand/collapse the org chart tree.

Things to consider improving in this MR (or in a future iteration):

• Better visual indicator that a node has a collapsed tree

I tried not to introduce another visual element to indicate collapsed/expanded state as the UI is already visually busy, but I'm not 100% convinced the current use of border/box-shadow is the best way (especially from an accessibility pov).

EDIT: Based on feedback the default state has been set to show the tree fully expanded.