Mandelbrot set added, bug corrected in formulae
AA for exported image, minor tweaks

performance (quite useless) in the generation loop, added a label to get
the iteration number for every pixel.
Minor bug corrected, and the end of NaN for Mandelbrot (performance hit
expected)
automatic detection of fractal type in combobox
minor optimization for julia, new (stub) fractal added
New fractal added : The burning ship !