Adds visbilityjs lib

What does this MR do?

Adds visibilityjs lib to our dependencies -> https://gitlab.com/gitlab-org/gitlab-ce/issues/29569#note_25990560

https://github.com/ai/visibilityjs

Usage

import Visibility from 'visibilityjs';

Visibility.change(function (e, state) {
    if ( !Visibility.hidden() ) {
       Poll.makeRequest();
    } else {
       Poll.stop();
    }
});

What are the relevant issue numbers?

Closes #29569 (closed)