Simple pvpstats command

This is a very simple command to let the player quickly see which is the faction which won most BGs in the last 7 days and have an idea of the server balance.

```.pvpstats``` will output:

![pvpstats_command](https://cloud.githubusercontent.com/assets/75517/4779667/87455cec-5c3e-11e4-9716-682d0528ec1d.png)

`fields1` and `fields2` do not have to be declared outside

```c++
Field* fields1 = result1->Fetch();
Field* fields2 = result2->Fetch();
```