Giving users of modal a chance to reference the underlying tiddler

To make it possible to reference the underlying tiddler from a modal the `currentTiddler` variable is set and made accessible in the `bodyWidgetNode`.

This way the user (programmer) gets a chance to access fields of the tiddler the modal is based on.
We try to avoid extraneous blank lines. There are some blank lines in the source where it helps readability, but for the most part we avoid them.