Clean up listeners on body from EventHandler

[mhevery]

Application rootNode defaults to HTML tag and any listeners attached to it will hang around accross all tests;
https://github.com/angular/angular.dart/blob/master/lib/application.dart#L147

In tests this needs to be overwritten to point to a new div each time:

Needs to be owerwritten here: https://github.com/angular/angular.dart/blob/master/lib/mock/module.dart#L53

[mvuksano]

@mhevery Isn't this already done?

Looking at event handler test,, it seems like a new element is created and it's used to override ``Node` in the module - https://github.com/angular/angular.dart/blob/master/test/core_dom/event_handler_spec.dart#L33

it's also destroyed after each test - https://github.com/angular/angular.dart/blob/master/test/core_dom/event_handler_spec.dart#L39

Did you have something else in mind?

[mhevery]

This is EventHandler specific. I wanted something which is global to all tests.