support non-corda CA tree

[woutslakhorst]

• [x] setup scripts for keys (also in nuts-network-setup)
• [x] configuration for extra keys
• [x] endpoints and logic (similar to how Corda handles it)
• [x] spec and docs on endpoints

[woutslakhorst]

see #43

[woutslakhorst]

ClosedBy #49