Added block for live rendering.

On update 0.5.0 i have added feature which block the render of canvas on each move end, which will save the lag when you are exporting huge images. To make this work you have to asign $scope.blockManagement={block: true} to . When you have to render the canvas into dataURL you just have to $scope.blockManagement.render(function(dataURL){console.log(dataURL);}). I have build live demo on the Codepen: Rectangle Crop;