added support for shape (currently rounded rectangle)

usage :
       local button = widgetExt:newButton(
        {
          x = xButton,
          y = yButton,
          width = buttonsWidth,
          height = buttonsHeight,
          labelAlign = “center”,
          labelAlignY = “center”,
          shape = {
              cornerRadius = 10,
              strokeWidth = 2,
              strokeColor = {default = {0.5,0.5,0.5,1}, over =
{0,0,0,1}},
              fillColor = {default = {0.8,0.9,0.8,1}, over =
{0.6,0.7,0.6,1}},
                },

          labelColor = { default=myApp.textButtonColor, over=
myApp.textOverColor },
          onRelease = onRelease,
          label = btn.caption,
          font  = myApp.font;
          fontSize = fontSizeButtons,
          onRelease = onRelease,
              });