TypeDB Visualiser bugs

[alexjpwalker]

The TypeDB Visualiser is now pretty good - it behaves like a regular force-directed graph, gradually converging towards a "natural" shape of the graph structure it represents. However, it isn't always perfect:

• [ ] The target distance between nodes is always measured from their midpoints. This works well for circular nodes, but poorly for rectangles: Maybe we should adjust the link force based on the length of the shortest edge connected to each node?
• [ ] Disconnected nodes tend to get pushed away from the rest of graph and disappear off to infinity and beyond.
• [x] We should truncate long labels. Currently it's possible for labels to overflow nodes.
• [x] Edges should be displayed under vertices, not over
• [ ] When there are two edges between the same pair of vertices, their labels are superimposed, which looks hideous. Should we create bendy labels or use a comma-separated list?

[alexjpwalker]

Split up into #464 , #465 and #466