Allowing for configurable default version

This change allows the API developer to choose which version should act as the default if none is specified in the URL or headers.

This is accomplished by setting `[zf-versioning][default-version]` in `module.config.php` (which defaults to `1`). If this setting is omitted, then the existing default value of `1` in the `PrototypeRouteListener` will be used.

I modified the `dataProvider` in the test class to provide an optional `$apiVersion` to allow for testing various possibilities, such as:
* Developer-specified default version of `1`
* Developer-specified default version of "not `1`"
* No developer-specified default version. (defaults automatically to `1` as is done presently)