Links should use current resource: 70%

This PR address #14: for tables, if _link_ was used in a joined resource, the link was always for the base resource, not the joined one.

It also addresses a problem where, in a scenario where there is a join defined, and a graph is added to tripod with a condition that matches the join, but the graph of the object of the triple had not yet been added, the URI of the join would not get added to impact index, so the table would not get updated when the object graph eventually got added.  Essentially, tripod tables and search were not respecting the open world assumption.

This PR still needs me to add documentation.
Some checks on the actual impact index itself?