Migrate to use Rubicon, rather than PyObjC

[freakboy3742]

This patch migrates PyAutoGUI to use Rubicon, rather than PyObjC. Rubicon is pure Python, and doesn't try to install the entire universe; it requires a little more configuration, but it's just as reliable as PyObjC, (in my experience, anyway; Toga uses Rubicon on both iOS and macOS).

Two notes about the patch:

• There are currently 2 keyboard tests failing - however, they were also failing for me under PyObjC:

======================================================================
FAIL: test_press (tests.basicTests.TestKeyboard)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/rkm/projects/pyautogui/tests/basicTests.py", line 562, in test_press
    self.assertEqual(response, 'ba')
AssertionError: 'a\x1b[Db' != 'ba'
- b
+ ba


======================================================================
FAIL: test_typewrite_editable (tests.basicTests.TestKeyboard)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/rkm/projects/pyautogui/tests/basicTests.py", line 536, in test_typewrite_editable
    self.assertEqual(response, 'c')
AssertionError: 'abc\x1b[D\x1b[D\x1b[D\x1b[3~\x1b[3~' != 'c'
- abc
+ c


----------------------------------------------------------------------
Ran 16 tests in 22.738s

FAILED (failures=2)

• It's Python3 only. Rubicon uses a bunch of Py3 features (most notably, type annotations). Besides, PYTHON3 IS THE FUTURE!! :-)

[afs2015]

@freakboy3742: Are you on OS X? I believe it's the same failing tests I am encountering here on #225.

[freakboy3742]

@afs2015 I am, and yes, those two are the same failing tests.

[asweigart]

Hey Russ! I will definitely take a look at this in the near future.

[freakboy3742]

Thanks Al! I've just updated the PR; the patch now passes all tests on macOS.