Update govuk_admin_template to 1.1.3

This fixes an issue where the GOV.UK brand would not display using the
correct font in Internet Explorer or Chrome on Windows. For other
changes check the changelog in `govuk_admin_template`.

Sass is also upgraded from 3.2 to 3.4 in this release necessitating
adding an explicit import of '_shims' before the mixin %contains-floats
can be used.

Sass's changelog
(http://sass-lang.com/documentation/file.SASS_CHANGELOG.html#backwards_incompatibilities__must_read)
doesn't specifically mention anything I can see that would cause this,
but it's two breaking changes difference.
Merge pull request #272 from alphagov/update-govuk-admin-template

Update govuk_admin_template to 1.1.3
un-aaib-ify; comment out some redundant features
Various changes to make progress on DSU import
Remove debugging puts statements
Remove date_of_occurrence code in DSU mapper. Causes issues with non-unique slugs.
Prune more AAIB-specific code
provide therapeutic area, obliterate Report from DSU classnames
provide summary import