Set Application controller default URL options to ensure all url_for calls are consistent

### What does this MR do?

This MR sets the app controller's `default_url_options` so that all `url_for` calls are consistent.

### Are there points in the code the reviewer needs to double check?

Setting these options may simplify `url_for` calls that load the GitLab options already. I did not want to touch existing code yet. I'm also not sure if there are other options that need to be included.

### Why was this MR needed?

If you run GitLab behind a reverse proxy or in a Docker container, you don't want a user to be seeing the local IP and port on which GitLab is running (e.g. 192.168.1.1:8080). Right now there are places where this internal data is leaked (e.g. see the URL in Profile Settings -> Account -> Username; this uses `user_url`).

### What are the relevant issue numbers / [Feature requests](http://feedback.gitlab.com/)?

#1249

See merge request !453