adx-1064 instructions button added to top nav menu

[tomeksabala]

Description

Draft implementation of making a link to Estimates Instructions more visible in the top header.

Overview of changes:

1. Updated helper build_pages_nav_main with latest changes from source ckanext-pages
2. Extracted logic for building localized URLs for pages (e.g. /fr/pages/fr-inputs-unaids) into a separate helper
3. Extended template header.html with list to Estimates instructions
4. Fixed bug in member_list.py encountered while updating string translations.

Note: This change needs to be published together with adding entry to ckan.ini:

ckanext.pages.about_menu = False

Checklist

Put an x in the boxes that apply to this pull request (you can also fill these out after opening the pull request).
You may not need to check all boxes.

• The Jira ticket for this issue has been updated to "Ready to Review" or equivalent.
• I have developed these changes in discussion with the appropriate project manager.
• My code follows the general Fjelltopp documentation (see Confluence).
• I have made corresponding changes to the Fjelltopp documentation (see Confluence).
• I have rebased this branch with master.
• New dependency changes have been committed.
• I have added automated tests that prove my fix is effective or that my feature works.
• New and existing tests pass locally with my changes.
• My changes generate no new warnings.
• I have performed a self-review of my own code.
• I have assigned at least one reviewer.

[jonathansberry]

You should fix the linting issue though...