Adds an additional draggable area around each knob

[felipericieri]

Hey! With this MR I introduce a way to increase the draggable area around the knob. It is useful if you have a knob smaller than your finger lol.

In order to use it, just update the property knobDraggableArea: KnobInset. An object of KnobInset type will accept a dx & dy axis. It is a property with a default value of 0.