Add support for localAddress option of net.Socket

[peschuster]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Feature

• What is the current behavior? (You can also link to an open issue here)
  It is not possible to bind the client to a local address.
  When multiple CasparCG clients run on the same host only one of them can receive OSC data from the CasparCG server, because CasparCG always sees the same sender address for the AMCP connection.

• What is the new behavior (if this is a feature change)?
  This feature allows to specify a local address for the casparcg-connection.
  Therefore a host with multiple addresses in the same subnet can run multiple CasparCG clients, bound to distinct IP adresses and therefore all receiving OSC data from the CasparCG server.

• Other information
  Tested with official CasparCG release "2018-12-29 - Version 2.2.0 Stable" and used in production at two multi day events during the last months with CasparCG as video playout server and generator for lower thirds with the following clients: https://github.com/peschuster/casparcg-hyperdeck

[mint-dewit]

The typings here should be string | undefined I think, since that's how you define it in the public interface

[peschuster]

I just copied the behavior/style of the host field, but I think your right: localAddress should probably not have a default value from the IPv4 address space. This might break attempts to connect to an IPv6 host. I will have a look at this but need to do some more testing.

[peschuster]

I fixed it and did some tests with the new default value undefined.