adding dockerfile, versions file and build script

- creating basic java base image
- adding build script
- adding gitignore
- adding dockerfile
- installing oracle java 7, oracle java8, openjdk 6, openjdk7
- setting oracle java 7 as default
I'm not sure `java` as a default command makes sense. We're doing it for python and node because that will get you in to the repl. Java will just exit immediately, right? Maybe `/bin/bash` is more appropriate?