Improve Viewer website menus

[blairlyons]

• [x] https://github.com/simularium/simularium-website/issues/297
• [ ] https://github.com/simularium/simularium-website/issues/347
• [x] https://github.com/simularium/simularium-website/issues/322

Use case

As a user, I want to be able to quickly, easily, and accessibly navigate menus on the Viewer website.

Acceptance Criteria

• Tooltips and labels are useful but not in the way
• Menus can be navigated with a keyboard
• Input box on Load by URL menu is automatically focused when menu is opened

[lynwilhelm]

Add to this list improve the timeout ghost gaps issue with menus