Add dependsOnContainerEnd opt: load next page if content's bottom reached

If you have no any nav/next elements, infinitescroll can't detect when you need to load next page.
So now you can specify next options:

    navSelector: false, // false allowed now
    nextSelector: false, // false allowed now
    dependsOnContainerEnd: true // new option

and next page will be loaded when you scroll to the end of the container's element.