By default display the time range with traces only

[stwhite91]

Original issue: https://charm.cs.illinois.edu/redmine/issues/1884

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When I manually insert traceBegin and traceEnd calls into my application to trace say a few iterations out of many, then open Projections on those traces, Projections will display the entire time period that the application ran by default. But only a small sliver of that is stuff that I actually care about. It would be nice to by default start the time range at the first traceBegin call and end it at the last traceEnd call.