Adding inputs option for "Search:" label

Hi ! 

I'm using dynatable for my website and I just saw that the label "Search:" near the search field is not easily changeable. 

So I create an option, just like you did at first, to modify the label.

I tested it just now and it's working great.

I hope it will fill your requirements.

Thank you for your work.

Added an input option to modify the "Search:" label near the search field.