Add support for LEFT_TRIGGER and RIGHT_TRIGGER on Logitech Dual Action controller in Webkit

On the Logitech Dual Action controller, the buttons below LB and RB were not mapped.

This PR maps them correctly as LEFT_TRIGGER and RIGHT_TRIGGER.

**Note:** A minified version is not provided. It might be best if the project adopts a build system, such as grunt, and uses that create a minified version from the source file.