Model chainloading

[beheh]

To prevent releases from the addon/game page to require a query to fetch the addon details every single time, the releases should offer the possibility of chainloading via a natural join - possibly even only instancing the actual addon model when required. Thus would greatly reduce the SQL query overhead.

[beheh]

The model class is now aware of fetches via fetch($model, $row) - chainloading should optionally be specified on presenter level, maybe via $model->chainloadAddon(), $calling this->chainload('Addon', 'addon')?

Then the last thing to do is to make the PersistenceService table-aware by prefixing, deserializing the chainloaded model and injecting it into the original model.