Better Entrypoint Support

In order to address #410 I'd like the ability to specify entrypoint parameters. This adds a new setting, dockerEntrypoint, which takes in a Seq[String] and passes that to the ExecCmd form ```"ENTRYPOINT"```. It keeps the default ```bin/executableScriptName``` in place.

On a sidenote, I don't understand the current usage of executableScriptName. This does change the entrypoint value, but it forces the script to be places in ```/opt/docker/bin```. It also doesn't change the outputted bin script's name. So it seems you need a specific script in a specific place in your container. I believe passing an ENTRYPOINT exec value is a more flexible approach.

Tests/documentation coming, but I wanted to get early feedback.

Thank you,

Mike