ActivityTransitionReceiver

There are several limitations on receiving activity transitions. The Intent passed in has to be mutable because it's altered by the Activity Recognition code to add in the transition events. However, to be mutable means that it has to be an explicit Intent which in turn means that it must be registered in the Android manifest and can't be registered dynamically using registerReceiver. In turn that means that ActivityTransitionReceiver can't take any extra arguments, so to get data out of here we use a singleton Otto bus.