Rename scenarios to scenario_sets

Each file in the scenario folder is not a scenario, but rather a set of scenarios
Add scenario_sets to the flow
Allow for question groups and multiple questions per page

Scenarios should test for question groups
Scenarios should visualise when questions are asked as part of one page
Expose name as part of question Api

In order to check that the right questions
are being asked for in the scenarios,
we need the name of the question to be exposed
in the flow
Allow scenarios descriptions to have space between # and text
Use Model objects instead of OpenStruct for scenarios
Update documentation to add scenarios

Remove "TBD" parts of the documentation
Update several areas of the docs to indicate this is no longer a spike
Merge pull request #72 from alphagov/scenario-sets

Scenario sets