Switch to work-in-progress new Task List component

[frankieroberto]

The "Task List" component is currently not part of govuk-frontend, and so there is currently a cross-government collaboration to bring it in. As part of this, there are a few design changes to improve usability and accessibility.

This is a preview of the work-in-progress design, so that we can get an early feel for it, and can potentially test it with candidates.

The main differences are:

1. the status appears capitalised rather than UPPERCASE to improve readability
2. the colour of the status label has been changed to hopefully reduce the number of people clicking on thinking that it is a button
3. the suggested status labels have changed so that the incomplete tasks are more prominent than the completed ones

Related links

1. Existing task list guidance on GOV.UK Design System
2. GitHub conversation about the existing pattern
3. Draft pull request adding the new task list component to govuk-frontend
4. Draft pull request updating the task list guidance on GOV.UK Design System

Screenshots

Before	After