Add logo - suppport PNG with alpha channel

[Grobe]

Hi.

The add logo filter currently only support jpg files. I have a png image with alpha channel that I want to use as logo. Why? Simply because it will look very cool and look more professional than using a JPG with typically white background that is not transparent.
Adjusting the alpha value down, doesn't remove the background color (wich in most cases appears as a rectangle/unwanted frame around the logo)


Thanks