Store execution time of Phylomemy graph
@anoe requested to add a field to the Phylomemy node to track the execution time of the algorithm, to serve as a "Visual Cue" for users, to know what to expect in terms of execution time.
If that's not too hard, we agreed it would be nice to store a list of the history of the executions, so that the frontend could take the average or just the last available execution.