Bug 1054326: Initial attempt to submit Imagecompare test framework and test cases int...

...o the main branch
ah, there's no documentation, I can add that in soon. In the meantime, the code is here: https://mxr.mozilla.org/mozilla-central/source/testing/marionette/client/marionette/gestures.py and example usage https://mxr.mozilla.org/mozilla-central/source/testing/marionette/client/marionette/tests/unit/test_gesture.py