Improved taxon admin view

I improved the taxon view in the admin and added a functionality to remove a product from a taxon using the API. Added tests as well.

To be more clear, some screenshots:
Before:
![screen shot 2014-12-26 at 15 00 07](https://cloud.githubusercontent.com/assets/106335/5558108/d3195bda-8d19-11e4-9746-f50b8fab670d.png)

After:
![after](https://cloud.githubusercontent.com/assets/106335/5558109/de03ad70-8d19-11e4-8c46-6ea2e4db6376.png)
Use `%` instead of `%Q`.<br>Do not use `%Q` unless interpolation is needed.  Use `%q`.<br>Use `%Q` only for strings that contain both single quotes and double quotes, or for dynamic strings that contain double quotes.