Feature request: legend

[psteckler]

In just a couple of days using spacetime, we've found a memory leak in our code. Great!

When examining a graph, some of the areas are very narrow, and hard to find with a mouse pointer. It might be useful to have a legend off to the side to make it easier to navigate the callstack.

The legend might consist of rows for each call site, where each row has a colored square or other shape, the same color as used in the graph, followed by the call site location, the same as shown in the tooltip in the graph.