aerie Add @AllChildren annotation

Tickets addressed: Part of #1364 but does not resolve it
Review: By commit
Merge strategy: Merge (no squash)

Description

Add a @AllChildren annotation to mission model so mission modelers can report, for a given activity, what other activity is called/spawned. This information will be used by the scheduler to evaluate whether it is useful to resimulate or not before goal evaluation: let's have G goal being satisfied by an activity of type A, G is the next goal to be evaluated. If an activity of type B was inserted at the last iteration, has B any chance of generating A and thus of satisfying the goal G ? If yes, simulation is required, otherwise it's not (for that only purpose, there might be other things that warrant a simulation, e.g. the goal needs to also evaluate an expression...).

Some edge cases:

If the user does not use the annotation for an activity, we make the worst case assumption that the activity might generate all activities (itself included).
Activities without effect model cannot generate children

This PR does not contain changed to the scheduler to use this information. These changes would overlap too much with changes under review in #1323