Multiple questions per page
* Remove API objects from SmartdownAdapter
* Implement presenters for Question, QuestionPage, PreviousQuestion, PreviousQuestionPage
* Presenters implement methods that shouldn't be part of the API and are required by templates
* Two animal example questions to demonstrate to demonstrate single-question and multiple-question behaviour
* Remove question numbers for all cases except multiple questions on one page
Merge pull request #1079 from alphagov/multiple-questions

[merge-after-smartdown-32-33-35]Multiple questions per page
Graph presenter
Merge pull request #1091 from alphagov/graphpresenter

Graph presenter
Graphviz presenter