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
Merge pull request #1092 from alphagov/graphvizpresenter

Graphvizpresenter
Correct label for multiple question responses in collapsed section
Use nil not 0 for absence of question number
Merge pull request #1099 from alphagov/use-nil-as-default-question-number

Use nil not 0 for absence of question number
Merge pull request #1098 from alphagov/response-label-multiple-bg

Response label multiple question bug
Graph presenter
SPL flow as specified in Google Drive
Corrections to match current smartdown syntax
Display date questions