Added LaunchRocket

**NOTE**: The caskfile is identical to that provided by the author, who is currently hosting the cask from his own `jimbojsb/homebrew-launchrocket`. I opened an issue at https://github.com/jimbojsb/launchrocket/issues/29 to notify the author as well.

---

A Mac PreferencePane for managing services with launchd/launchctl.
LaunchRocket was primarily created for managing various services
installed by Homebrew, though it should work with most
launchd-compatible plists.