Allow 0.0.0.0 as bind address

Currently, bind_addr has to be a valid interface and the wildcard (0.0.0.0) address is not permitted. The reason is that bind_addr determines the physical address of a node, e.g. 192.168.1.5:46537, and using 0.0.0.0:46537 wouldn't allow us to identify the node in order to send it a message.
To allow for TCP and UDP sockets to bind to the wildcard address, we could either use a bind_addr of 0.0.0.0 and introduce an additional property to pick the physical address (e.g. physical_addr="192.168.1.5" / physical_addr="GLOBAL"), or continue using bind_addr to determine the physical address and add a property (bind_to_wild_card_addr="true") to make the UDP and TCP sockets bind to the wildcard address (if true).