feature: yAxisLabel

Feature: provide ability to set y axis caption - rotating should be handled by svg, because not all browsers can provide transformation for span/div for labeling.
[![Screenshot](https://drive.google.com/uc?export=view&id=0B65dEGRmB3ViWDV4NEtuMXZDS3c)](https://docs.google.com/file/d/0B65dEGRmB3ViWDV4NEtuMXZDS3c/edit)
Given next options:
```
...
        yCaption: {
            offsetX: -30,
            text: 'THIS IS A VERY LONG Y CAPTION',
            fSize: 15,
            fFamily: 'Arial',
            fWeight: 800,
            color: '#123'
        }
...
```