Feature: Product Metas

This pull request adds the ability to define and attach custom product meta data. New Product Meta concepts have been added and the control panel's product configuration tool and the related product APIs have been significantly updated.

__Concepts Summary__
 * __Product Meta:__ A meta name definition (e.g., Size)
 * __Product Meta Option:__ A meta value definition (e.g., Size: Large)
 * __Product Option Meta:__ A meta option attached to a product option (e.g., Luxury Touch Polo -> Size: Large)

Each Product Meta can have one or more Meta Options. And there is a many-to-many relationship between Meta Options and Product Options.

__Control Panel Summary__
The Control Panel Product pages now include a left nav, similar to the Customer management pages.

![products](https://cloud.githubusercontent.com/assets/1553251/5024313/1c08aad0-6ace-11e4-871d-983a7887f1c8.png)

![metas](https://cloud.githubusercontent.com/assets/1553251/5024317/2472dd3a-6ace-11e4-9a74-995d46046b4f.png)

![meta-options](https://cloud.githubusercontent.com/assets/1553251/5024318/26aa4b6a-6ace-11e4-9a8e-a21616e1e389.png)

![product-metas](https://cloud.githubusercontent.com/assets/1553251/5024320/29957098-6ace-11e4-9472-a23aaf701e7f.png)

__API Summary__
Meta data is included in ```/api/product/{id}/options``` responses and two new endpoints have been added:

```
/api/products/{id}/metas
/api/products/{id}/metas/{id}/options
```

Currently, there is no way to delete a product meta or meta option. Planning on adding this functionality at a later date as it will involve properly handling cascading deletes/updates for relational data.