Refactor toolbar and `GraphInterface`'s state

[dburian]

Toolbar

The toolbar should be:

• reusable with configurable buttons and orientations to be used in more than just one place
• floating above the content

The current toolbar has also some problems:

• no animations
• sticky slider -- e.g. too much graph should be interpreted as a full-screen graph

GraphInterface's state

Spaghetti code of mixing url-based state and persistent state. The current toolbar needs to understand GraphInterface's state to work.

[dburian]

With 8fecae8:

• more reusable
• not floating -- If it was floating above the graph, it wouldn't be visible with full-screen note.

The state management is hard:

• we need to coordinate the URL with the correct state, suggesting URL should be the source of truth
• but we also need to persist some states between pages
• it is doable within the component, but the code becomes very messy
• I tried (99bdf3e12de4cb9e1be547244a82c2c23f6dd8bd) to extract the logic to a store, but this introduced another source of truth (URL and store), which has led to flashes of content

Currently, I've settled for a simple Toolbar without any slider, as I don't really need it. I'll add some animations and see what we end up with. Maybe then I'll include the slider.