Separating BBP events into its own library

The library will be temporarily located here.
The toggle request event has also been added until a better solution is found to handle the selection state when multiple applications are involved.
I'm not sure about ToggleEvent. I initially had a similar name, but it's misleading because the toggle hasn't happened yet, this message requests the selection manager to toggle a list of IDs.

I don't like SelectionIDEvent, it's also ambiguous. What about SelectedIDsEvent.