Change recommending passphrase_entropy to zxcvbn

As @edwardhorsford noted in Campfire, we don't really use the library
that we recommend here. So we should change the manual to reflect
real life.

https://govuk.campfirenow.com/room/412745/transcript/message/1169471680
Move breadcrumb related Sass into single file

This also fixes a layout issue on the search page.
Various content changes requests completed

- Added 3 new case studies with accompanying text to 'increasing
digital take up'
- Added Digi comms lead JD to recruitment page
- Updated content on 'digital take up'
Merge pull request #306 from mattedgar/patch-1

Add new dates
Merge pull request #307 from alphagov/update-passphrase-entropy

Update passphrase entropy page and fix Sass issue
Remove '(required)' label text

As this contradicts our current guidance on marking optional fields.
Merge pull request #308 from alphagov/content-revisions

Various content change requests completed
Add ideal alpha guidance
Correct spelling and capitalisation as requested
Reword long sentence
Add Alpha navigation
Add link from alpha page to ideal-alpha page
Remove common questions

Need to design better content.
Merge pull request #311 from alphagov/remove-common-questions

Remove common questions
Restructure old content

Add back the links to the content, but in a way that can be read quickly and
easily.

Needs to be in HTML rather than Markdown for $reasons.
Merge pull request #312 from alphagov/content-improvement

Restructure old content
Use current content style guide URLs
New page requested by Sarah Richards

This is a template, so includes empty links eg [full privacy notice](link)
Apply content style guide
Fix meta data so that document appears in index pages