First test runs of Node+Bootstrap, big bug fixed

FIX: bracket hOpen hClose (fork ...) closes the handle immediately after
     forking. Both the server and the bootstrap server did this, leading
     to dead handles instantaneously.
Dirty debug commit

Lots of "print" messages scattered over the code here. Bootstrapping
works, but neighbour search doesn't; the network is not yet stable on
its own at all.
Bootstrapping works for first of 2 nodes

- Client housekeeping temporarily disabled
- First node finds second one up-/downstream, second one finds nothing
Monomorphic send/receive, misc stub edits
Some signals moved from normal to special
Node type wrappers introduced

Incoming addresses are now wrapped in 'From', outgoing ones in 'To'. The
distinction makes it impossible to accidentially connect to a 'From'
address; 'To' addresses are the only ones storing actually running
server addresses.
Bootstrap server: node wrappers added
Removed 'debug' print statements
Changed server workers from IO () -> IO Proceed

This feature was previously removed, I then found out it's a pretty bad
idea to either terminate workers immediately after messages have been
sent or never, leaving them running indefinitely. :-s
Known vulnerabilities section
Visual check for Server.hs correctness, refactored
Merge branch 'node_direction_types'