modules/assets: add a wrapper for getDimensions in texture object

gamecore/modules/assets/texture.lua

@@ -42,6 +42,10 @@ function Texture:new(filename)
   self.mask  = love.graphics.newImage( maskData )
 end
 
+function Texture:getDimensions()
+  return self.image:getDimensions()
+end
+
 function Texture:draw(x, y, r, sx, sy, ox, oy, kx, ky)
   love.graphics.draw(self.image, x, y, r, sx, sy, ox, oy, kx, ky)
 end