Revision 1815579

[Component-DSL] Add new branching primitives

These branching primitives will allow to discriminate according to the
incoming values and generate different branches that will be able to
keep their own state, like aggregations or highest values.

The difference with a flatMap is that the latter always _spawns_ new
producers though making it impossible (at least with the current
implementation) to accumulate the highest service references
discriminated by some property.

I don't know if the fact that I had to introduce these primitives is a
signal that I am missing some generalization that could make all these
primitives subject to be abstracted out.