Adds possibility to add a callback to ChainFind.find() (#190)
Forces .findByX() to have conditions and passes callback to Model.find() only if defined (#190)
Changes Model.find() to check if cb is really a function (and not just "not null")
Passes original table to possible conditions in merge queries (JOINs) (#190)
Improves test-association-hasone-findby to test ChainFind.find()
Fixes previous change to use table in conditions. This needs to be passed by .find()