Include local source in Dockerfile and add .dockerignore.

Resolves #97

Building on your change in the 0.96.0 branch.

I split up the `ADD` steps so that you don't have to repeat the install of grails and all the dependency libraries unless one of the dependencies actually changes. This way, when you make a code changes, re-building the war in the docker image is nearly as fast as it would be locally (just re-compiling the files).