Replace --port with --listen

[davecgh]

Instead of only accepting a port to listen on, the cli parameters should allow the user to specify listen interfaces.

Examples:

Flags	Comment
--listen=	all interfaces on default port which is changed by --testnet and --regtest (This is the default)
--listen=0.0.0.0	all ipv4 interfaces on default port which is changed by --testnet and --regtest
--listen=::	all ipv6 interfaces on default port which is changed by --testnet and --regtest
--listen=:8333	all interfaces on port 8333
--listen=0.0.0.0:8333	all ipv4 interfaces on port 8333
--listen=[::]:8333	all ipv6 interfaces on port 8333
--listen=127.0.0.1:8333	only ipv4 localhost on port 8333
--listen=[::1]:8333	only ipv6 localhost on port 8333
--listen=:8336	all interfaces on non-standard port 8336
--listen=0.0.0.0:8336	all ipv4 interfaces on non-standard port 8336
--listen=[::]:8336	all ipv6 interfaces on non-standard port 8336
--listen=127.0.0.1:8337 --listen=[::1]:8333	ipv4 localhost on port 8337 and ipv6 localhost on port 8333
--listen=:8333 --listen=:8337	all interfaces on ports 8333 and 8337