Fix initial aspect ratio when not responsive

Fix initial aspect ratio when not responsive

When responsive is false and no canvas height explicitly set, the aspectRatio option wasn't applied because of the canvas default height. Prevent the retinaScale method to change the canvas display size since this method is called for none responsive charts, but instead make the resize() responsible of these changes. Also, as discussed some time ago, moved most of the core.js logic into core.controller.js. Clean up the destroy process and make sure that initial canvas values are properly saved and restored.