Add meta-graph interaction

[Mercotui]

The meta-graph should be interactive, to allow the user to explore the solution space.

1. Clicking on the graph should select the nearest dot as current state
2. ✅ Clicking and dragging the graph should translate the graph.
3. Scrolling on the graph should zoom the graph in/out

Split off flickable translation to #24.

[Mercotui]

Requirement 2 was completed in #23