Fix module description colouring
Remove h2 wrapping description

It is defined in the template and doesn't need reopening.
Add 100% stacked charts

Allow any stacked graph to be set up as a 100% stacked. Apply this to
the device usage graph on the GOV.UK dashboard.
Update line labels to reflect data being displayed

On a 100% graph the data being displayed is the percent so should be
written first. This swaps them round. It also unifies the logic for
printing them out.
Handle missing data points

If data comes back empty then nothing should be displayed. Previously
this was causing missing data points to be given the average available.
update data-group to government
Rename dashboard to govuk rather than dashboard

It better reflects what it is.
Remove 100% graph from carers
Remove extra header and fix markup

- Description is wrapped in a header in the template. Don't need to in
  the stagecraft stub
- Typo in the group0 span causing it not to be recognised
govuk -> gov-uk
Fix test dependant on classes and null objects

In some situations the model might be null, it should be checked for
The no-data class was needed when there is no-data.
Merge pull request #150 from alphagov/govuk-dashboard

GOV.UK dashboard updates