Consistent tooltips and hover cards

[nikolausWest]

There are currently two types of tooltips / hover cards in the UI: tooltips that describe something in the UI, and data previews that show up when you hover over data. The hoverable ?s that describe how to navigate in different space views are a huge visual eyesore but are potentially useful to some users.

In the future we may also want to have a way for users to log "entity descriptions" like "The output of our confidence estimation network" that could show up when you hover over a Space View or entity path.

TODO @martenbjork:

• Fill this out with a design suggestion