New (template) classes: BasicNode, NodeServer; deleted ProtocolNode

This is a rather big commit.

  * BasicNode replaces ProtocolNode.  There's a small difference in their
    template parameters, so have a look at the updated tests/live-test.cc
    for usage.

  * NodeServer provides server functionality for slave nodes using the TCP
    protocol.

  * The "default" callbacks previously in tests/live-test.cc have been
    formalized as defaults in comms/bits/MessageDispatcher.tcc.  See
    comms/MessageDispatcher.hh for some doc-comments on what these default
    handlers do.
comms/common.hh: need an #include <thread> for THREAD_ID macro...
tests/live-test: some changes that didn't make it into @bbf51af
comms/NodeServer: workaround for broken Configuration copy constructor