Revert "Rework Stapfen to use OnStomp instead of the Stomp gem for better JRuby compat"

The issue has since been fixed, waiting for an upstream version release

This reverts commit ec822fd433f61626154ad62dd6816f9a9af24df2.
Add the `log` method to the DSL, allowing easy use of log methods from within the worker

Bumping the version to 1.2.0 for the next release too because hey why not