Share events.js between cordova and plugman

Currently there are two instances of events.js under cordova and plugman folders which provide exactly the same functionality.

https://github.com/apache/cordova-lib/blob/master/cordova-lib/src/plugman/events.js

https://github.com/apache/cordova-lib/blob/master/cordova-lib/src/cordova/events.js

This is common functionality which must be shared among cordova and plugman so must be moved to some common folder (src/events.js???). Similar to CordovaError and xml-helpers.js

It is also required to be able to reference to 'events' from shared code - as an example, common Hooks code which emits messages via 'events'.