Add funcationality to specify the amount the value should be incremented...

.../decremented, ex:
![for_github_comment](https://cloud.githubusercontent.com/assets/4966393/4146976/bb523a04-3412-11e4-9290-a91a00b0f336.png)
We set a value of 10 for 'data-step' attribute, so the value of this number picker will be increased/decreased by 10 every time. If user doesn't set this attribute, it will use 1 by default.