Bug 1023087 - [Window Management] Marionette test for copy-paste

https://bugzilla.mozilla.org/show_bug.cgi?id=1023087
->
```
test('click top-left input', function() {
  fakeTextselectionApp.press('bottomLeftInput');
  var textSelectionLocation = fakeTextselectionApp.textSelection.location

  assert.ok(
    textSelectionlocation.location.y <
    fakeTextselectionApp.bottomLeftInput.location.y,
    'dialog should be placed higher than the input field'
  );
  assert.equal(
    textSelectionLocation.x, 0,
    'dialog should be placed near left boundary'
  );
});
```