script.js: refactored
	modified:   script.js: made private getImageById, selectImage;
			       renamed selectImageById to selectById;
			       renamed getSelectedImage to selected
script.js: Images: added g to group images under cover
script.js: removed useless loading variable
script.js: refactored: decouple cover logic to class Cover
	modified:   script.js: Cover: added;
			       open,close,adjust,before: added;
			       renamed cover, uncover to hide, unhide;
script.js: refactored: decoupled circles logic to Circles
	modified:   script.js: added Circles;
			       removed getIndicator;