Make section_id values consistent
Better title tags for sections and update pages

Currently, every page in a manual has "Manual Title - GOV.UK" for the title
tag. This isn't very helpful if you had multiple pages within a manual open at
once.

This change prepends the section ID for HMRC Manuals, the section title for
non-HMRC manuals or the word "Updates" for update pages.
Merge pull request #108 from alphagov/better_title_tags

Better title tags