Rudder

In rules details, we have a nice way of managing Groups which are the target of the Rule.

We should display Directives in the same way, because for now, it's kink of hard to see what directives are applied when the tree is big.

So, we should:
- add a green (+) on directive mouseover:
- add a zone on the right with the list of active directives for the rules, with a X to remove them
- have a message when no directive is selected for the rule

Moreover, with that, we could close the directive and group tree by default (or just let one level opened).