Add item IDs to each item on the code quality checklists

[sarahcollyer]

Feedback from UKHSA:

It would be nice to have a unique ID for each item, that will be the same for everybody using the Duck Book.

As an example, this is what I have done. I have created an excel sheet with all the items and given them unique reference numbers.
L – Lower list

1. – First section of the list
   01.1 – First item of the first section
   And used this system to allow new items to be added in new versions.

I think it would be good to have something like this in place, to make parts of the checklists easier to reference.