Update to latest Robotlegs 2

Just thought I would update this extension so it is in line with the changes made recently to RL2. 

This consisted of:

* Replacing references to `Injector` with `IInjector`
* Updated the `CommandPayload` package name.

Also I sneaked in a `.gitignore` file just so any artefacts created by the Ant build script aren't accidentally committed.