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`.

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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.