"Help" mode for the visualizer

The visualizer is getting to a stage where it is packed with functionality, but we don’t have too much explanation for what everything does.

We should have a “Help” toggle button, which when enabled, will show hover tooltips on all datapoints, buttons, and any other points of interest.

For new users visiting the visualizer for the first time, we should highlight the button that toggles this mode.

One of the main challenges with this is making sure that it doesn’t hinder our other users; it should be easy to disable, and obvious to see when it is enabled.