Unconditionally insert shop link via PHP

This patch causes the Wikimedia Shop link to be inserted via PHP irrespective
of geolocation. Clickthroughs from countries which the shop does not service
can be handled on the shop's page, instead. The JavaScript link insertion code
is retained as an interim strategy for the 30-day period following deployment
of this change during which cached pages may not contain the shop link.

Rationale:

- Changes to the user interface that cause the page to flicker or reflow after
  page content has already loaded prolong user-perceived latency by postponing
  the time at which the interface is complete.
- The shop link module loads in the top queue, meaning the byte size and
  parsing overhead of its payload block page content.
- GeoIP lookups are performed by adding an HTTP request above the fold, meaning
  it blocks the rendering of content. Fundraising banners are allowed to use it
  as a special case, but other extensions may not, as this complicates the
  process of keeping the loading of GeoIP to a minimum.

Bug: 57939
Change-Id: I92dac7589013636b500d0ec6e22fc5a72e264e84
Merge "Unconditionally insert shop link via PHP"