Detect already running BusKill apps

[maltfield]

This issue will track the effort to add a check to the BusKill app to detect if another version of BusKill is already running.

I discovered with @goldfishlaser that somehow she ended-up with a version of the BusKill app still running (visible in ps), but it was not visible in the GUI. The result: she noticed that BusKill was triggering even when the (redundant) GUI app showed that it was disarmed.

When we killed the other buskill process, the "issue" went away.

Solution: We need some way for the BusKill app to check to see if another version is already running, and warn the user if-so.