Where to mount, where the dialog is, and the defaults.
A handle, or null when there is no Extensions API to talk to,
initialization failed, or the extension is not running in a dashboard. A
handle whose current options leave nothing to mount still comes back, with
binding set to null, since the next settings change may fix that.
Run MAIDR as a Tableau dashboard extension.
Initializes the Extensions API, reads the options saved with the workbook, and mounts MAIDR for the dashboard's worksheets into the extension's page. Filter, data, parameter and layout changes re-read the worksheets; a change to the saved settings rebuilds the figure from the new options.