Add iframe/window management

[everzet]

I will implement 2 new methods in DriverInterface:

• switchToWindow(…)
• switchToIFrame(…)

First one will switch window to some specific one, second one will switch to specific frame.
By providing no argument to this functions - you will be switched to base_window/out_of_iframe.

Sahi and Selenium will support this, but Goutte and Symfony will not - they will simply throw
exceptions as always. Not sure yet bout Zombie.js.

[markct]

Is there currently some other way to switch windows? Even a dirty workaround? I desperately need to be able to do this.

[antranapp]

+1 for this. Some Richt Text Editors use frame to render text and it's quite difficult right now to test when using these elements