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* Add item option to remove padding from images dropped on a zone.
* Add option to show zone border when dragging an item.
* Hides text when a draggable item is placed in a target zone and frontend wait for LMS response, this is done since the size of the item increases when the spinner is visible.
* Change containers and css classes to match those from edx-platform. The problem div now contains the drag container, buttons and feedback, css classes from submit button; submit answer and action buttons were also changed.
* Improve feedback styles, now only icons shows color related with feedback and text color remains the same also each feedback line doesn't show borders.
* Replaced `Travis` with `GitHub CI`.