Added cool new IB options!

* You can now specify a RGBa color using "colorString (String):
255,128,0,0.5" (r,g,b,a) in the Interface Builder
* You can now specify the image pattern offset by setting "offsetString
(String): 10,0" (x,y) as an NSPoint
* You can now activate corner radius for every corner using
"roundedTopLeft (BOOL): YES / NO" (TopRight,BottomLeft,BottomRight
respectively), set the radius using "cornerRadius (NUMBER): 5"