Use of links between containers should be deprecated

As discussed in #463, docker networks seem mature enough to use, and links are officially not recommended any more.

We'd like to deprecate use of links; off the top of my head I believe we ought to do the following things:

• Obviously, mark the container addLink method as deprecated with a clear comment
• Links aren't currently documented very well, but update the docs with a clear enough description of the networking support, so that ad-hoc linking can be done easily by users
• Modify Webdriver VNC recorder sidecar container to remove use of links
• Modify Docker Compose support; can we remove use of the ambassador container now?

まず Docker Compose のサポートと ambassador コンテナの使用箇所を追跡し、次に関連するテストと現在のネットワーク動作を調べます。Compose ベースのテストを壊さずに ambassador を削除できるかどうかを判断します。そこですでに links が不要になり、既存の Compose サポートが合格するテストによって引き続きカバーされていれば完了です。