The function KisNode::copyFromNode() is to copy the data from
another node into the current node. We will use this function
for new undo commands for vector layers. This should be a
temporary approach until we make the whole KisDocument implicitly
sharable. At that time we will only need the copy functions of
KisDocument and KisImage.

This is an experimental commit and may not work thought it does
build.

Task: https://phabricator.kde.org/T10901