Individual steps duration in feature report

I went ahead and implemented a feature which I wanted for this plugin, that is the display of duration for individual steps. For every successful step, the duration is displayed on the right-hand side of the row, formatted in seconds/milliseconds (or larger values, but I hope your tests don't run for that long). I also updated the existing unit tests to reflect this change, although I did not add any more, as I did not feel it was necessary. I will add more if requested.

I don't know if this is of interest to other users of this project, but I'm currently using it to detect which specific steps contain performance issues when inspecting a report.

Please excuse the reorganizing of imports in my second commit, Eclipse seems to enjoy doing that and I only realized after I pushed.