As described in the readme but not implemented until now, this patch
enables the skin version to be specified as a URL query parameter. This
is useful for testing both skin versions during development and on wiki,
as well as enabling sharing URLs with a specific skin (Vector) and skin
version (1 or 2).
Obtaining the actual skin version requires tying together three input
sources, WebRequest, User, and Config. It seems simple but it'd be easy
to botch. For this reason, a helper class to correctly interrogate them
and tests are provided.
Bug: T244481
Change-Id: I52d80942b4270c008d4e45050589ed9220255a50
