Added isRunning

[idontusenumbers]

I needed a way to check if a launchd job was running or not. I made a new method (or whatever they are called, I'm new to ObjectiveC). I figured others might find it useful.

[eahrold]

@idontusenumbers, there is actually a function in AHServiceManagement https://github.com/eahrold/AHLaunchCtl/blob/master/AHLaunchCtl/AHServiceManagement.h#L54 ,

If you want to proxy that function in AHLaunchCtl, I’d be fine with that, just update this PR

[eahrold]

@idontusenumbers you still want this?

[idontusenumbers]

Ah, I didn't see that one. I'll switch to that method. I think there's some inconsistency there but I'm too new to ObjectiveC to make a call on which option is best. Feel free to reject the PR, no hard feelings.