R1:efc82c727bb4

Measure how long build targets take in Harbormaster

Summary:
Ref T1049. This keeps track of how long a build target takes to execute in Harbormaster and displays it in the build view page. I'm not sure whether "Started" is really that useful once the target has completed?

Also, I change the name of the time taken depending on whether or not the target has completed; if it's still in progress it's called "Elapsed" and if it's completed then it's "Duration". The primary reason for this is that…