Update to newer style of styling and template

- Use the header-footer-only template, this doesn't need the styles or
  JavaScript for the mainstream formats.
- Update govuk_frontend_toolkit for the new grid-layout mixins
- Use govuk_frontend_toolkit mixins for a global wrapper width
- Move content_for tags to the top of the template, so it is clear when
  you look at a template how that template effects the parent template
- Move the page specific sass to a partial Sass file (partial files have
  leading underscores) and put it in a view folder so its scope is
  obvious.
Add byebug for debugging in development
Move browse over from frontend and style

- Moved over the functionality from the browse controller on frontend
- Created views for those pages and styled as per designs
- Copied over the tests from frontend and refactored them to work with
  the new code. Added a couple of cucumber tests to hit parts the
  controller test didn't.