Updated Apigility Admin to allow setting of the default API version

See [zf-versioning:PR #1](https://github.com/zfcampus/zf-versioning/pull/1)

Thoughts @weierophinney? My only concern is that there is no visible confirmation that the default version has been changed once the user changes the SELECT option. Perhaps a `confirm("Are you sure you want to change the default API version?");` (or something prettier)?

On the other hand, they'll see it in the `git diff` for their module before committing the changes, so the lack of a visual confirmation right now isn't the end of the world.

**NOTE:** [This assertion](https://github.com/michaelmoussa/zf-apigility-admin/blob/933725e2f4453dd24e59641e096199c45780090a/test/ZFTest/Apigility/Admin/Model/VersioningModelTest.php#L167) will fail until [this PR](https://github.com/zendframework/zf2/pull/5569) is merged. I inadvertently introduced a BC break with the readable PhpArray config writer change. :/