Pin screen

These changes build on those in PR #65 and are trying to get Payments working again, so only the 2nd commit is relevant. I am able to get through the "Create PIN" screen, but cannot seem to automate the "Confirm PIN" screen, which is quite strange.

What seems to be happening is that when the "Continue" button is tapped, taking us to the Confirm screen, they keyboard goes away and I cannot seem to make it come back no matter what elements I tap on the screen via Marionette.

I need to abandon this for now, but hopefully @AndreiH, perhaps with some help from @davehunt, will be able to get past this issue which will bring us very close to having payment testing reenabled.
  
@bobsilverberg I was able to workaround this issue with <code>self.marionette.find_element(*self._pin_container_locator).click()</code> it seems that tap does not work, click works just fine bringing the keyboard back up