include ViewHelpers into ActionView::Base

as when requiring WillPaginate 2.3's 'will_paginate'

Change-Id: Ifd4d711d55203c9131e7dd5e5edd644a02e81a22
treat a provided page of nil as if not provided

so paginate(page: nil) is the same as paginate() (which is the same as
paginate(page: <first page value>)).

this makes nil a special value, unusable as a page value. I think that's
reasonable, and this behavior lets clients do stuff like paginate(page:
params[:page]) without needing to worry themselves over whether
params[:page] is nil or not.

note that {page: false} is still a usable page value.

Change-Id: Ie4afed914501c97aaef87a55f2279f3a16fc262e
Merge branch 'master' into legacy

Change-Id: I63a7c48f30d74ea01726f8bfae2a95bb039ecfbc
Merge "Merge branch 'master' into legacy" into legacy