Implement global event dispatcher

[bartaz]

There should be one global shared object where all the events will be registered and triggered to remove unnecessary dependencies between modules.

[gustaff-weldon]

Observable class already in place
addEventListener(eventName, listener)
removeEventListener(eventName, listener)
fireEvent(eventName)

Right now used as mixin, it should not be hard to resign from mixing in, just reference as global singleton. Yet, I think event source will be needed in event data