fixed #10 by adding theme to preloader modal.

Fixed #10 applying theme to the modal and make html image theme-able by replacing html img src with css background image. 

Note: Currently, the loading gif for Light and Orange are dummy gif. Since the image is not processed by html or css, please give it the correct theme and replace `../img/light/preloader.gif` and `../img/orange/preloader.gif` respectively.