Refactor title and context into module

[fofr]

Clean up each format’s template by moving format specific logic into module, with overrides in format presenters.

Default:

• Content item title
• Context based on document type
• Long title length

This makes it difficult to include titles with the wrong attributes.
It also makes it easy to link to translations to any format – if a format has translations, then the links will display – protecting against accidental omission as with the speeches format.

One further commit:

• Protect against overwriting properties on the other hash provided to metadata and document footer components

A template for a standard format is now as simple as:

<%= content_for :page_class, @content_item.format.dasherize %>
<%= content_for :title, "#{@content_item.page_title} - #{t("content_item.format.#{@content_item.document_type}", count: 1)}" %>
<%= content_for :meta_description, @content_item.description %>

<%= render 'shared/title_and_translations', content_item: @content_item %>
<%= render 'shared/withdrawal_notice', content_item: @content_item %>
<%= render 'shared/metadata', content_item: @content_item %>
<%= render 'shared/description', description: @content_item.description %>
<%= render 'shared/sidebar_with_body', content_item: @content_item %>
<%= render 'govuk_component/document_footer', @content_item.document_footer %>