Set max width to images wich are linked in the href

This Pullrequest improved the possibility to resize the Images wich are shown in a Lightbox or in a new window.

The Reason why I need this is, that I am working on an extension, wich resize the Images for mobile devices. With these changes it would be much more easier to resize those images.

I use the `$GLOBALS['TL_CONFIG']['maxImageWidth']` beacause it overrides all other Image width as well.

One Thing I am not sure if we should resize this as well. -> the original `$objTemplate->singleSRC`.

What do you think?