Issue/2499 kif integration

Added KIF integration to the project.

The UITests are now in a separate scheme called UITests to not interfere in the WordPress scheme and on the current Unit Tests.

Before the tests are started you need to configure and add  .wp_test_credentials to your home folder. This file needs to have user and passwords to use in the tests.

Before you start the tests you need to logout all users and self-hosted sites from the simulator and disable the hardware keyboard on the simulator ( Just Press CMD+SHIFT+K).

cc @sendhil