Javascript modal dialog changes

Uses JSON to call help_text.php.

The diff display makes it difficult to see what I've done, but I've modified modalDialog(), helpDialog() & modalNotes to use jQuery to create a DIV element with title & html attributes populated by whatever call method is appropriate and then pass that element to a new function displayDialog() which instantiates and displays the dialog and handles clicking on the overlay and tidyup on close (which at least one of the old functions didn't - can't remember which off hand)