Splitting outputs from logic operators

[hasanbalci]

Moved from sbgn/process-descriptions#159 since it is actually related to Activity Flow.

The issue was previously mentioned in this discussion:
https://groups.google.com/forum/#!msg/sbgn-discuss/JAiPkj883CM/7uwVwbv5DAAJ

[adrienrougny]

As mentioned in the discussion, while the issue is relevant, the example is not (it makes no sense to represent metabolic processes as the one above in AF).

[hasanbalci]

Augustin: Allow some of these but only in simple cases. Rupert is uncomfortable with potential implications.

[adrienrougny]

@cannin @rupertoverall What would be those allowed/not allowed and what could be the undesired implications?