BUG Revert some changes to ManyManyList

This fix reverts some changes made in the ORM rewrite of 3.2 to ManyManyList, as well as fixes some issue raised as the result of some behavioural changes in testing. Notes will follow on the individual line items.
This whole section has been reverted to pre-rewrite format since DBFields rely on `$manipulations` in order to inject values.