Allow completed tasks to be saved and displayed when requested !

Leader Task deletes tasks as they are completed. For our business, we need to retain the completed tasks along with their start and end times. This is an absolute must.

For us, it wouldn't matter if the completed tasks were always displayed, but controls could be added to toggle display/hide completed tasks and delete completed tasks, just in case someone else using the application doesn't want them.

Multiple tasks in any timeframe is also important, and PDF export would be nice as well.