[wip] Update pixel and object classification for 1.3.2

[k-dominik]

fixes https://github.com/ilastik/ilastik.github.io/issues/28 Summary:

• Pixel Classification:
  • [x] use specifiable sigmas + 2d/3d documented
  • [x] updated screenshots
• Object Classification
  • [ ] updated screenshots
  • [ ] document object features fixes #4, fixes #5
  • [ ] document table export

[k-dominik]

closing this in favor of #73 and #72