Remove `_unflatten` method

We're not using it
Add checks `NaN` in volumetrics target percentage

- check if number and finite
- return `false` --> 'no data' if not, add no-data class
Return `false` if value is `NaN`

- Don't show 'processed within' line if we're not showing any data
remov
Merge pull request #860 from alphagov/bugfix/applications

No data view for applications module