Task plot improvements

I have updated the plotting script and the output of the task data such that we can now have the full information for a given time-step and not just the last call to engine_launch(). This means the drift tasks will now be included in the plots. They will also include the single-core part where the cells and tasks are reconstructed. The start and end time as well as the CPU frequency are dumped in order for this to work.

Also, added a cosmetic change to the output for the case where a snapshot gets dump.