INFRA-95 Display extension version compatability on main node
Use the node update hook to copy version compatibility from extension release to main extension node. Aggregate this info so the main node contains all tax terms from its children. As a side-benefit to this, the main node will be updated every time a release for it is saved - that way the "last updated" field (displayed on https://civicrm.org/extensions/) will reflect the most recent release date (currently it only displays the last time the main node was edited, which is misleading).
Original author: colemanw