Allow one to specify the karma value and coefficient names in settings.

* Adds two new helga settings:
** `KARMA_VALUE_NAME`: Name of karma value.  Default 'karma'.
** `KARMA_COEFFICIENT_NAME`: Name of karma coefficient.  Default 'karma coefficient'.

If we're going for the 'meowmeowbeenz' theme -- I'd suggest adding the following two settings to our helga config once this is released:

```python
KARMA_VALUE_NAME='MeowMeowBeenz'
KARMA_COEFFICIENT_NAME='5 Factor'
```