Unxfail tests that reply on Test Zippy with Me app

Bug 1043838 has been fixed
Merge pull request #53 from bobsilverberg/unxfail

Unxfail tests that reply on Test Zippy with Me app
Settings button locator changed on new UI
Merge pull request #54 from AndreiH/settings_button

Settings button locator changed on new UI
Xfail test_marketplace_login_during_purchase.py with Bug 1058529 - [marketplace-tests-gaia] Investigate test_purchase_app is failing on Jenkins
Merge pull request #55 from AndreiH/xfail_pay_test

Xfail test_marketplace_login_during_purchase.py with Bug 1058529 - [mark...
Switch tests to login using Firefox Accounts, instead of Persona
Updates to allow the code to run with the latest gaiatest