Fix/givekarma display

Fix to- https://github.com/marc1706/phpbb3-ext-karma/issues/10
Now that the links have changed from real icons to just text for this, I'd go for just removing the icons for giving positive/negative karma.

Also please change the language variables to this:
```	'GIVEKARMA_POSITIVE'				=> 'Give positive karma',```
```	'GIVEKARMA_NEGATIVE'				=> 'Give negative karma',```