For outbound connections, since they are initialized by the users, we
can relax on the restriction. A future global limit may be added - as
for now, we will let them to be managed by the users.
When a peer already has a connection with us, there's no need to check
for available slots as we will either close the old conn or refuse the
new conn.
Here we introduce the access manager which has caches that will
determine the access control status of our peers. Peers that have
had their funding transaction confirm with us are protected. Peers
that only have pending-open channels with us are temporary access
and can have their access revoked. The rest of the peers are granted
restricted access.
