Bump to version 4.2.1

Use a shared cache between shared templates and skin templates so that
they all update together.
Merge pull request #86 from alphagov/version-bump

Bump to version 4.2.1
Remove lrucache include

The dependency on it was removed in d0a963c8 but it was left in as an
include.
Merge pull request #87 from alphagov/remove-lrucache

Remove lrucache include
Version bump to 4.2.2

Remove unused include
Merge pull request #88 from alphagov/version-bump

Version bump to 4.2.2
Add a Search-Parameters header

This allows apps to add extra parameters, which will be submitted along
with any search entry made from the page.  They get transformed into
hidden input elements in the search form.

This is part of https://www.pivotaltracker.com/story/show/77617490 -
there'll be a follow-up PR on whitehall which emits a header value to
filter search results by organisation for some pages.
Merge pull request #89 from alphagov/search-parameters-header

Add a Search-Parameters header

https://www.pivotaltracker.com/story/show/77617490
Automatically insert report-a-problem into the wrapper

Before this change, each app had to add a `div` somewhere
that `slimmer` replaced with the report-a-problem form. With this change,
the form is inserted as a child of the wrapper without any extra markup being
needed in the app itself.
Add header which disables report-a-problem form addition
Slimmer::Skin: refactor wrapper variable to avoid duplication