Debt Free Day Integration: add dependency to the Gemfile
Debt Free Day Integration: update schema.rb after running migrations
Debt Free Day Integration: make sure the engine inherits the correct controller / layout
Debt Free Day Integration: add a Cucumber feature to test integration
Debt Free Day Integration: save cassettes after running Cucumber feature

These cassettes cache the API calls made for categories when running the
Cucumber feature for the new engine.
Debt Free Day Integration: create a ToolMountPoint and mount the engine

This tool mount point needs to be able to expose routes for 2 separate
calculators. The changes required to achieve this were:

* override the `match?` request matcher method
* override `alternate_tool_id`
* make it clear `en_id` and `cy_id` are not supported as there is no
  single tool id for this tool mount point
Debt Free Day Integration: wrap in a feature block.
Debt Free Day Integration: add bower dependency on the engine
Debt Free Day Integration: JavaScript integration
Debt Free Day Integration: update schema.rb after rebasing on e675e4b