Persist: Entity collapse/expanded state across sessions

[davidpuetter]

Would be nice that when you collapse/expand entity groups in the editor, their open/close state would save so when you restart, the hierarchy stays the same. In addition to this, a "collapse all" and "expand all" button to open/close all entities recursively in a group would be nice!

The same goes for entity components, too. Would be nice if they retained their open/close state.