feat(scenario):  add mouseover method to the ngScenario dsl

so e2e tests are more readable.
- it adds a mouseover() method to element that trigger the mouseover
event on that element.

Motivation: I wanted to write a test that checks that the method in
the ng-mouseover directive was correct.

````coffeescript
it "should display the user friends when mouseover the avatar ", ->
  element(".user-avatar").mouseover()
  # ...
````