Adding Generics support for the underscore functions throttle, debounce, once, after

When I do something like this:

var handleScroll = _.debounce((e:JQueryEventObject)=>{
    //Handle the scroll event here
});

$el.on("scroll", handleScroll);

Typescript compiler throws error citing parameter mismatch.

Since these functions return the function with same signature as the functions passed in it is easy to support them via generics.