HG-309 Use click event to close a lightbox instead of tap

There was an issue that closing lightbox in Mercury sometimes result in redirecting to `Special:UserLogin` if below the close button site header is visible. First approach was to [create a workaround which was hiding site header when lightbox is displayed]() but it introduced a dependency between lightbox and site header which we didn't want. It also wasn't "immune" to changes in 3rd party library we use (headroom).

In this pull request I've moved firing `closeLightbox` method from a tap event to regular click event which should solve the issue.