Fix initializer for `relationshipLocal` configuration

[themightychris]

The spot where the many-many relationship option relationshipLocal is supposed to be initialized suffers some copy-pasta duplicating relationshipForeign instead:

emergence-skeleton/php-classes/ActiveRecord.class.php

Line 1865 in 7504a36

if (empty($options['relationshipForeign'])) {

It looks like as long as warnings are disabled, this mistake only results in the two uses of relationshipLocal being a no-op which are avoided if consumers of saving to many-many functionality only set already-configured link class instances

This bug is a good time to start building out ActiveRecord's core unit tests, merge a fix for this that includes a unit tests that goes from failing to passing