Added user stats panel

Added a panel to the right sidebar on user profile pages and user script listings, that contains some stats about that user.

The panel contains the following stats:
* Number of scripts
* Number of libraries
* Total installs
* Avg. installs
* Avg. rating

Other stats can be added in a next PR.

Screenshots:
![userstatspanel profile](https://cloud.githubusercontent.com/assets/55841/5236125/25174310-7826-11e4-9dbb-54d6482c27f7.jpg)
![userstatspanel scripts](https://cloud.githubusercontent.com/assets/55841/5236129/311ee190-7826-11e4-8d35-c6c2c7e4ba26.jpg)