Decide how to integrate firewalling

[robertvolkmann]

The first iteration was removed by #40 to help third parties become familiar with metal-stack.

[vknabel]

Due to the fact that firewalls are currently unmanaged and that they make use of the node network, we are unable to freely reconcile the node network and decided to make it part of this issue.

#55 makes the node network mandatory and might need to be reverted in the scope of this issue in the future..

[vknabel]

We already tackled this topic in the MEP16 and prepared it in #119 and #118