Fixed usability issues in the Crop Tool

Here is the list of changes:

1) Now you can restart the crop rect by click-dragging outside
of the current crop rect. Just start dragging a new rect and
it will replace the current one.
2) When activating the tool, the crop rect is created automatically
*only* if you have some global selection active.
3) If you "click" on the image, the whole image will be selected
4) If you "click" outside of the current crop rect, it will be deselected
automatically