More improvements to handling empty data

There are two improvements to how empty datasets are treated in this release:

1. When template elements are extracted from the document, but then are never bound to, the template parent elements have their innerHTML set to an empty string. A major benefit to this is that :empty is more reliable for using in CSS to display a message such as "This list has no entries yet".
2. Binding nested data where inner leaves are "empty" are treated in the same way when using bindNestedList as with bindList.

Have fun!