Improve legend in detail view

[wlach]

@bwinton had some ideas on how to improve the legend interactions. Putting them into their own issue for now, will probably split off some subtasks soon:

• group "other" into right panel as well (instead of giving everything it's own item)?
• maybe give legend a different background color (or put into well)
• merge legend w/ graph? (maybe, not sure if this is a good idea)
• build ids are long? truncate them? have full thing show on hover? make buildids look more human-readable?
• if there's only one version, automatically group by buildid
• handle series with no data better (automatically skip somehow?)