Improve UI/UX around selecting a single bar

[Rperry2174]

We improved this a little bit in #621 but I think we could potentially make the UI/Ux around selecting a single bar even better. Especially when the timerange is short (i.e. < 30 minutes) I think that we could make it so that:

• the bars are wider
• you can click on a particular bar to show flamegraph for that bar
• you can "unclick" a particular bar to go back to the flamegraph for the full timerange selectd

I think this could improve the UX because when you select a single bar, you can no longer see the context around that bar because of how the drag-and-select functionality works.