Need a category view for the entire range, not just for the selected node

Usually, when I'm looking for category percentage information, I want to know the percentages of the entire runtime for the selected thread. So at the moment, my interaction with the UI usually goes like this:

1. Select the thread I'm interested in.
1. Open the sidebar.
1. Sigh.
1. Scroll up in the call tree and click the root node.

I think the fact that the sidebar shows information for the selected call node by default, and the fact that there is no alternate view to show a breakdown for the entire runtime, is a problem.

I'm not sure how to fix that. Maybe we could give the side bar two tabs? One, selected by default, that shows data for the entire runtime, and then another for the selected call node?

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-174)