IsolatedScope & Two-Way Binding for specific attributes

Hi @seiyria 

Thank you for your powerful slider and your directive.

I've modified your angular-bootstrap-slider directive as follows:

* An isolated scope and a two way binding for the following attributes 
  * max
  * min
  * step
  * value
  * ngModel
  * range
  * sliderid
* On the OnSlide Function I've added the parameter 'value' with the actual slider-value.

I don't know whether it's a good solution - it's my first modification on an existing directive. Can you give me a feedback? 

Please check the example (text.html) for the usage.

Regards, patrick