shiny/widget/node: add a nextSibling arg to AppendChild.

Also rename AppendChild and RemoveChild to Insert and Remove.

Change-Id: I4a2200054ddae0d2174943c7a0d5da2a084cb451
Reviewed-on: https://go-review.googlesource.com/23743
Reviewed-by: David Crawshaw <crawshaw@golang.org>
3 files changed