Fix parent position when walking child nodes

[mbrgm]

The child node needs to know its parent's absolute position in order to
determine its own absolute position. Previously, the parent's relative position
(in relation to its own parent) has been passed. This leads to wrong
positioning of nested nodes after several levels of recursion. I fixed this by
passing the current node's absolute position to the child nodes' layout
function.

[mjohnston]

Looks like a good fix. If you don't mind, could you take a second to fill out the CLA and I can pull this in.

The css-layout stuff is not really baked. It has perf issues and doesn't support text flow. Not sure if you're up for it or not, but PRs in this area are welcome :)

[mbrgm]

Done. What would be an alternative to css-layout? I like the intent of it quite well.

[mjohnston]

Alternative (which is what we use on flipboard.com) is to absolutely position everything. This is the default behavior if you don't specify enableCSSLayout on the root Surface. It works out ok for us since our layouts are paginated, and doing multi-line truncated text regions with flexbox is not possible as far as I know.