Emit event when bottom is visible

[leighhalliday]

When the bottom is visible, emit an event so that a listener can know it is reached and act as a signal to load/append additional IDs to the bottom of the list.

It would be great if this could be configured so that when it is X records from the bottom it emits event.

[sakin]

I'm thinking of also adding in the ability to show a loading element, not going to spend too much time on it, but want to see how hard of a lift it is