Hardcoded `servers` definition makes swagger UI usage not possible, when using a load balancer

[Ocramius]

I'm aware that StraightMail was designed to stay within its own VPC network (not exposed to the outside), but in a dev environment, it is not uncommon to make the HTTP traffic available to the host, either via:

• port forwarding
• ngrok-alike tunnel
• traefik and Host header routing
• path routing
• etc...

The current API location (according to swagger UI) is hardcoded:

straightmail/src/main/java/com/encircle360/oss/straightmail/config/ApiConfig.java

Line 17 in 7fa62c9

url = "http://localhost:50003",

Perhaps that can be dropped, letting swagger use the current host as server URI?