stbt.Keyboard.add_transition: Take `mode` paramater as a shortcut
stbt.Keyboard.add_transition: Take `mode` paramater as a shortcut

So that you can say this:

    kb.add_transition(grid[-1][0].data, " ", "KEY_DOWN", mode)

instead of this:

    kb.add_transition({"name": grid[-1][0].data, "mode": mode},
                      {"name": " ", "mode": mode},
                      "KEY_DOWN")

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester