[SCAL-466] Hiding labels in histogram chart

![hidden](https://cloud.githubusercontent.com/assets/3713860/5424747/d143771c-82fd-11e4-9999-8f2d4f577e85.png)
![visible](https://cloud.githubusercontent.com/assets/3713860/5424746/d141fbb2-82fd-11e4-9760-58c3e485f99f.png)

Toggleable. 
Also when resolution >= 15 labels are hidden.