Issue: XF2.x: Migrate wiki statistics to a dedicated widget

It would be awesome if VaultWiki statistics could make full use of the XF2 widget system. Possibly something for VW 4.2?

I use the first-party addon XFMG which provides its own statistics widget. As media stats are in their own block, having wiki stats added to the same block as the forum stats looks a bit strange, IMO.

How I vision this change is:
1. The new dedicated VW statistics widget would have its own local toggle option for whether to include the latest wiki update.
2. options[vw_stats_block] would be retired from the "VaultWiki: Miscellaneous" options group.

If other customers would prefer to retain the ability to show wiki stats in the same block as forum stats, options[vw_stats_block] should still become a widget option in XF's default stats widget. When I want to configure a widget, the first thing I look for is a widget option in the Appearance > Widgets area of the Admin CP.