allow override of default duration for period queries
add stub response for vehicle-excise-duty failures
add vehicle-excise-duty failures collection
add vehicle-excise-duty failures table view
add failures table modules for tax-disc and SORN to vehicle-excise-duty dashboard
add vehicle-excise-duty channels stub response
add vehicle-excise-duty channels collection
add vehicle-excise-duty application channels graph
add vehicle-excise-duty services stub response
add vehicle-excise-duty services collection
add application services graph to vehicle-excise-duty dashboard
Merge pull request #154 from alphagov/vehicle-excise-duty-failures

Vehicle excise duty failures table
Merge pull request #156 from alphagov/vehicle-excise-duty-volumetrics

Vehicle excise duty volumetrics