Icon-step images are in a folder

The icon-step images were moved into a folder[1]. Update the Sass to look
for them in that folder.

[1]: https://github.com/alphagov/govuk_frontend_toolkit/commit/e523d51536482f3f300b798883c348e9d41bf2da
Merge pull request #1774 from alphagov/icon-steps

Icon-step images are in a folder
Remove IPO from the services & info page whitelist

Due to some content issues, we're removing the link to the Services & 
Information Page from the homepage of the Intellectual Property Office
at the current time.
Merge pull request #1775 from alphagov/remove-ipo-from-services-info-whitelist

Remove IPO from the services & info page whitelist
Reinstate keyword-filter identifier.

Removed in a previous cleanup the containing element for the keywords
field on all document filtering needs to have a filter specific
elementId.
See:
https://github.com/alphagov/whitehall/commit/4c682d099fa0f77f042d01bcd39c5dd9d44f317d#diff-08e4a107c3401662ebf39b86de38b01cL11
Merge pull request #1777 from alphagov/fix_document_filter_text_search

Reinstate keyword-filter identifier.