[Paraview] Overloading Mandelbro in PointSprite Plugin

[Isamu Yamashita]

Hi all,

Mandelbrot source was overloaded when I loaded PointSprite plugin
in paraview 3.8.1. I saw two Mandelbrot sources in the menu Sources
when I loaded it. It may cause some confusion in paraview.

In PointSprite_Rendering.xml, the class vtkImageSpriteSource was
labeled Mandelbrot.

I don't know the reason why the class had to labeled Mandelbrot,
but i think it would be better for the class to use other name
instead of Mandelbrot or to change ProxyGroup name in which the
class belongs from "sources" to "internal_filters".

Thanks,
Isamu