document graph traversal reimplementation for developers

Documents the changes to server code brought by https://github.com/openmicroscopy/openmicroscopy/pull/3228; some of the links may remain broken until it is merged. Mostly staged at http://www.openmicroscopy.org/site/support/omero5.1-staging/developers/Server/ObjectGraphs.html.
--no-rebase
Is this another Safari-ism? In Firefox I get,
![table](https://cloud.githubusercontent.com/assets/2630707/5229370/4b7916b4-770e-11e4-807b-16630fdd0bb6.png)