Add recipe to install Open JDK 8

I tested a few java builds and everything ran fine.

@BanzaiMan feel free to drop 9c466abb39ec8ae91a838454f7760c6ced5ea044 (additional jdk_switcher aliases)
Not sure about `7` designating the OpenJDK7, since the default is Oracle JDK 7.

(And this would propagate to `6` and `8` by analogy.)