implement modifiers on family icons

[oliver-sanders]

Task modifiers (e.g, "held") apply to tasks, they may bubble up to the workflow level and be displayed in the workflow sidebar (namely "held" and "retry"), however, they are never displayed on families (or cycles which represent the "root" family).

This has been highlighted as a regression from Cylc 7 where the "held" and "retry" modifiers were implemented as task states causing them to be reflected in the aggregate family state.

I don't think this omission was ever intentional, can't remember a decision not to do this, I think it just slipped the net.