Use localhost instead of 0.0.0.0 for webpack-dev-server

[catskull]

Resolves #424

[renchap]

A bit of explanations here:
0.0.0.0 is a special IP address. It should only be used in an HTTP server setting: listening on 0.0.0.0 means listening on all IP addresses available on the system: your LAN IP address, localhost (127.0.0.1), …

It should never be used to connect to an HTTP server. You need to use a proper IP address, like localhost/127.0.0.1, your server's public IP, …

From what I understand, dev_server.host is used to configure both the IP webpack-dev-server listens to (so 0.0.0.0 is correct here) and the host used to create assets URLs (and 0.0.0.0 must not be used here).

This setting should be split in two, maybe host and listen_address.

For local development, we can have:

host = 'localhost'
listen_address = 'localhost' # or 0.0.0.0

For remote development (for example Cloud9, the use case which prompted this change), we can use:

host = '<Cloud9 environment public IP>' # The one you use in your browser to
                                        # connect to your Rails server
listen_address = '0.0.0.0' # Webpack needs to listen on all addresses

[gauravtiwari]

Superseded by #482