Allow nested checkboxes to be collapsible

Expands the API of the macro to allow nested
checkboxes to have a summary tracking the current
selection, the fieldset to expand/collapse and
buttons to be added to allow jumping between
states.

Includes making 'Done' button inline on mobile.
Helps differentiate it form the form submit.

gulpfile.js

@@ -95,6 +95,7 @@ const javascripts = () => {
       paths.src + 'javascripts/previewPane.js',
       paths.src + 'javascripts/colourPreview.js',
       paths.src + 'javascripts/templateFolderForm.js',
+      paths.src + 'javascripts/collapsibleCheckboxes.js',
       paths.src + 'javascripts/main.js'
     ])
     .pipe(plugins.prettyerror())