Allow setting model attributes of array type.

[ghost]

Consider the following code:

$model = new ModelName;
$model->foo = [ [ 'foo' => 'bar', 'baz' => [ 'foo' => 'bar' ] ] ];
$model->save();

Here we are setting a nested array as a model attribute.
Before this commit, the code above would have saved the "foo" property as an empty array.

[pi0]

There are breaking changes on master so unitTests are failing. would you please follow This steps to rebase this PR with master branch and running UnitTests against latest changes ?

Thanks :)

[pi0]

Nice idea :D related to #926
@jenssegers would you please review this PRs ?

[pi0]

@dmitrimaltsev tests are added, would you please merge dmitrimaltsev#1 ? :)