Stress Metric Prototypes

Added a few new training stress metrics whilst discussing
and working on a multicomponent view of training stress.

This is all a wip falling out of discussions around stress
metrics beyond the old TSS/BikeScore models.

For now this just includes;
1. Aerobic Training Impact Scoring System on PM/PMC
2. Work (Kj) above/below CP on PM/PMC
3. Aerobic TISS on the Ride Plot

There is lots more to come; specifically around Anaerobic TISS,
looking again at polarised training and personalised training stress
based upon the individual's CP model.