Rewrite guidance and update examples

Conflicts:
	service-manual/assets/images/header-footer/header-pattern-1.png
	service-manual/assets/images/header-footer/header-pattern-2.png
	service-manual/assets/images/header-footer/header-pattern-3.png
Update example border style

Conflicts:
	service-manual/assets/stylesheets/design-patterns/_help-popup.scss
	service-manual/assets/stylesheets/helpers/_examples.scss
Small rewrites based on feedback from front-end dev
Typo and improve layout of HRs

Conflicts:
	service-manual/assets/stylesheets/views/_design-patterns.scss
Add header
Simplify copy
Add guidance on the blue bar and default width
Remove line after chat with Tom B
Simplify guidance around headers and footers
Add section seperators
Make HRs place nice with left columns
Update page subtitle
Add guidance about pre-beta services
Add example footer image and further guidance
Resolve conflict