Updated draft standard

I have updated the draft to:

* Add a table of contents
* Include slightly more preamble
* Bring the conceptual model up front, and then restructure the later sections to break it down in more detail
* Restructure the publishing model section into some worked examples to illustrate how the conceptual model might be implemented, and put in some specific questions about this
* Add other explicit questions for consultation in the document - to emphasise the consultative nature of this draft
* Added a short next steps section
* Add a credits section (this might need some other people named in it...)
* Added an image for the contracting journey (URL might need changing when deployed: I'm not sure how the current scripts for publishing this handle that).

I've made use of a few bits of bootstrap HTML, but tried to keep this minimal.