small adjustments
small adjustments
+ added execution start and execution time capture for steps and scenarios
+ altered IProgressNotifier.NotifyScenarioFinished() to accept IScenarioResult
+ added IProgressNotifier.NotifyStepFinished()
+ extended ConsoleProgressNotifier to display execution times for steps and scenarios
+ used ExecutionTime pretty formatting in ConsoleProgressNotifier
+ added ExecutionTime to PlainTextResultFormatter
+ added ExecutionTime and ExecutionStart to XmlResultFormatter
+ added ExecutionTime to HtmlResultFormatter
+ made ExecutionTime and ExecutionStart nullable