ol.MapBrowserEvent: call browserEvent.{preventDefault|stopPropagation}
Add ol.MapBrowserEvent.stopOtherInteractions

When called, stops the interaction chain.
API doc strings for preventDefault and stopPropagation

thanks @elemoine
Merge pull request #791 from fredj/mapbrowserevent

ol.MapBrowserEvent: call browserEvent.{preventDefault|stopPropagation}