[Feature] Add Cutout transform (#1022)

* Fix typo in usage example

* [Feature] Add CutOut transform

* CutOut repr covered by unittests

* Cutout ignore index, test

* ignore_index -> seg_fill_in, defualt is None

* seg_fill_in is added to repr

* test is modified for seg_fill_in is None

* seg_fill_in (int), 0-255

* add seg_fill_in test

* doc string for seg_fill_in

* rename CutOut to RandomCutOut, add prob

* Add unittest when cutout is False