With the parent of this commit (current master)
Loading the RevisionSlider JS without it expanded increases
the request size by roughly 767KB on first request and 242KB
on subsequent requests.
The large size of the first request is mainly down the to
dependancies of the slider.
This lazy loading patch means the RevisionSlider JS
only causes an increase of 184 KB per request.
If the user has the bar expand by default the main JS will
be loaded straight away (and the lazy JS will not be).
This patch also means that when only the bar is loaded the
pin button to set auto expand will not be shown.
This will be added once the RevsionSlider is loaded.
Bug: T151668
Change-Id: I054a82e9ea2aa89326464632e744497239f7adba
