Update ekko-lightbox.js

fixed a number of issue:
--modal was too big for small screens, fixed by setting a 'max-width' rather than a 'width'
-- images inside the modal were smaller than the actual image because borders and padding were not properly taken into account
--added logic to resize videos down for smaller browsers, keeping the proper aspect ratio
--the height property for videos is not really necessary as the aspect ratio is always the same, only a width is needed