bundle: support tracked relations

[erichanson]

Right now, every row a bundle tracks has to be explicitly tracked via tracked_row_add(). However, if you just want to track all rows in a particular table, a reasonable scenario, there's no way to do that with a single rule. Add support for tracked relations.

function bundle.tracked_relation_add(meta.relation_id) tracks an entire table (or view for that matter, as long as it has a unique pk), and inserts into a bundle.tracked_relation table. The bundle.tracked_row view would need to look at bundle.tracked_relation and dynamically add new rows. bundle.stage_row would need to automatically add new rows, I think?