Multi item licence

Changes:
- licences quantity assigned to (asset|user)
![image](https://cloud.githubusercontent.com/assets/351535/4457415/b844f976-4896-11e4-8fe3-f366598c4a3e.png)

@xliiv @quamilek please review.

I think above methods are redundant since: https://github.com/allegro/ralph/blob/develop/src/ralph/ui/channels.py