Fix typo "ceate" to "create"

Raise clear error if last training weights are not foundIf using the --weights=last (or --model=last) to resume trainingbut the weights are not found now it raises a clear error message.

- Update ROOT_DIR depending on path of file
- Remove unneeded __init__.py files
- Remove setting matplotlib backend

* create package mrcnn
* move notebooks to samples

If the mask is a rectangle, its mini-mask pixels
become all 1s, and it has no zeros. Scipy imresize
fails on that and returns 0s instead. This update
fixes the problem.

function cv2.rectangle, cv2.circle and cv2.fillPoly returns None.