Corrects errors when new methods added to EventEmitter.
Since EventEmitter is really a class with behavior, it should be extended, rather
than implemented as an interface. This enables new behavior to be inherited, e.g.
EventListener.prependListener() was added in Node 6.
* Add NW.js Definitions File
* Add NW.js Tests File
* Rename nw.js.tests.ts to nw.js-tests.ts
* Fix tests of nw.js-test.ts fails
Tests of `nw.js-test.ts` fails because `nw` was declared as module not namespace.
* Final fixes for tests failures
Fix below issues:
1- no reference to nw.js.d.ts
2- not defined some variables types (item: line 91 - screen: lines 136, 140, 144 - optional: line 167 - msg: line 230 )