Enables drag-and-drop behaviour in Shiny apps, by exposing the
functionality of the 'SortableJS'
JavaScript library as an 'htmlwidget'.
You can use this in Shiny apps and widgets, 'learnr' tutorials as well as
R Markdown. In addition, provides a custom 'learnr' question type -
'question_rank()' - that allows ranking questions with drag-and-drop.