chore(to_event_map): extract to helper and move constants to EVENT_NAMES
chore(helper): extract MapSpec and MapPropTypes to define event names
fix(Map): bind event once to component instance
fix(create_child_component): event binding for child components
Merge pull request #7 from tomchentw/refactor/map-and-fix-clear-listeners-issue

refactor/map and fix clear listeners issue