Refactor get tagline script so it doesn't require modules to have a dashboard type of other

We want to be able to have a configured tagline without forcing a specific dashboard type, so we add a fallback of just having a tagline property on the model.

Ideally we'd also get rid of the "other" stuff, but it stays for backwards compatibility.
Add support for high-volume-transaction option as dashboard-type
Merge pull request #414 from alphagov/refactor/get-tagline

Refactor/get tagline
Added transaction explorer dashboard generator.
Added high volume transaction dashboards.
Fixed description fields for dashboard.

Added notes sections.
Added digital take-up module generator.
Added digital-take-up for high volume services.
Added percentage format to digital-takeup
Fix issue caught by the schema validation.

Only add a related link if one is available in the response.
Fixed weird character issue
Trim whitespace
Changed dashboard-type as per @lennym request.