egui widgets are nice because there are many helper methods on the
egui::Ui struct for adding widgets to the screen in various ways. For
example, add_sized which designates an area to paint a widget. This is
useful in the note_contents case, as it allows us to reserve
available_space-20.0 pixels of the available area, saving 20.0 pixels
for a side-actionbar popout.
I'm not sure I'll use the side actionbar yet, but I've been
experimenting with that as an option to save vertical space in the
timeline.
I still need to make the side actionbar into a widget as well. It
currently uses the CollapsingHeader widget, which is designed for
expanding elements vertically. We may need to make our own widget for
animating an horizontal expansion if we want to achieve a similar effect
for the side actionbar.
