Unable to style vertical and horizontal grid resizer

[mpondo]

Although it is possible to apply a default style to all instances of the LayoutGridResizerControl, our styling team had the desire to apply a custom style to only the vertical style.

There are no hooks for setting the style for the control and the control is created within the code. It would be nice to add the ability to set those styles by exposing them as properties.

I have submitted this pull request as a possible solution:
#274