Revert "[python] install in a gladys folder"

This reverts commit a46502673433989658c5ed253a5c5401918d5078.

Does not work, I did test the former robotpkg install =D
[robot] update comment in robot model
drop the (opt) dep. on libpng

Let Python and PySide do the dirty work of graphical user interfaces.
[python] add gdal.get_band_as_uchar

float2rgb -> i8u2rgb