Not handling action blocks

[VolkerStolz]

Currently, we're ignoring action blocks and don't transform them:
http://cpntools.org/2018/01/09/code-segments/
Not a big loss for our examples and can easily be added by just making it a keyword to the transformation.

Examples are in discspcpn (where it's trivial) and NatCPN (where it's almost trivial: there is actually an of-then-else in the block, and I don't think we lose much).