Rename package and group

As part of the goal to submit deproxy to maven central, this PR changes both the package names of the classes and the group id of the module from "org.rackspace" to "com.rackspace". The reasons for this are two: 1. I checked about half a dozen other JVM projects in [rackerlabs](https://github.com/rackerlabs), and all of them used "com.rackspace", and 2. Maven [suggests](http://maven.apache.org/guides/mini/guide-naming-conventions.html) that the group id match a domain we control, as per the [Java SE 5 spec §7.7](http://docs.oracle.com/javase/specs/jls/se5.0/html/packages.html#7.7).

`mvn clean test` passes without any failures on my machine. A regex search for the old package name (`grep -irn 'org.rackspace' *`) turns up nothing. I clicked on every single link in the rst pages, and a good many of the links in the groovydoc pages, so I'm sure I got everything. If I missed any files, let me know.