Make median filter works with mask
This MR makes median filter works with mask by ignoring NaNs while computing the median for each pixel. To do so, it replaces the median filter of xsocs by a copy of the (updated) one from silx. This copy can be removed once silx 0.9 is released.
It also includes a minor fix for the bootstrap.py script that was not working with updated entry_point definition in setup.py.