Clean up Phoenix bar.

A lot of very cool new functionality has been added, but this has had the consequence that the Phoenix menu bar (the bottom bar) is becoming very full. Before we make a new major release, I think we should try to clean this up (because it is potentially a breaking change, if clients have suppressed some of the interface options).

The default menu is defined here: https://github.com/HSF/phoenix/blob/main/packages/phoenix-ng/projects/phoenix-ui-components/lib/components/ui-menu/ui-menu.component.html

We still want to keep the main options easily accessible, so we need to balance a little having it compact and still usable.

Options could include:

• Move the dark/light theme into "View options"
  • Orthographic/perspective could in principle go there too, but I think it should probably stay at the top level as it is very useful and you might want to rapidly click it off/on
• Browsers
  • We could move Event collections, Event Browser, and Geometry Browser into one top level menu

Thoughts @sponce?

Start with packages/phoenix-ng/projects/phoenix-ui-components/lib/components/ui-menu/ui-menu.component.html, which defines the default menu. Review the current grouping and the proposed View options and Browsers groupings, then agree on a compact, usable arrangement that preserves the main options and accounts for clients that may have suppressed interface options.