The change makes "weave expose" to call the "/expose" HTTP
endpoint implemented in router which exposes the bridge.
Such architectural change required as we need to know whether NPC is
enabled when exposing the bridge and weaver knows this fact the best.
Unfortunately, this change makes impossible to "weave expose"
when weaver is not running.
Otherwise, we risk to lose peer list when any failure happens after
the creation but before storing the list and as a consequence,
the weave container gets restarted.
Reworked interface to router so we split setting up the initial list
from beginning to make connections - we shouldn't do that until
after router.Start().
This is mostly a matter of moving some files, changing package names,
changing some imports, and changing some type references.
We duplicate the odd constant & global var, and the intmac/macint
functions, since neither 'router' or 'mesh' nor, really,' common' are
a natural home for them.
Bryan Boreham