Add Testing plugins

[devernay]

We need testing plugins:

• 4 plugins which support all combinations of tiles and multiresolution
• a plugin which doesn't support renderscale
• a plugin which give different images at each renderscale
• a plugin which returns isIdentity=true on the left side of the image, false on the right side (for testing isIdentity's renderwindow)
• a buggy plugin which write garbage in the output image outside of their renderWindow
• a plugin which returns infinite region of interest for any renderWindow
• a plugin with infinite RoD