adding augmentSQL & augmentWrite on ManyManyList

[tylerkidd]

ManyManyList was missing augmentSQL and augmentWrite
functionality, therefore limiting capabilities of using DataExtensions.

[tylerkidd]

Previously Scrutinizer tests were failing... merged in recent 3.1 changes and creating a new pull request.

[tractorcow]

I think we need to take care; augmentSQL and augmentWrite are actually extensions on the dataOBJECT not on the dataquery, datalist, or relation. If you check the code in DataQuery you'll see that the usage relegates this to the dataobject.

$obj = Injector::inst()->get($this->dataClass);
$obj->extend('augmentSQL', $query, $this);

If you want to augment relations, then it's ok to add API, but the context of this is very different to that of the augmentSQL / augmentWrite that exists in the codebase.

I suggest making a completely independent set of extensions which can be added for HasMany and ManyMany relations, and have those extensions added to the foreign class.

I also suggest you demonstrate an example of code that would benefit from these extensions; One which would not be possible without them?