Update docs images to match the new colorway

[k-dominik]

With the merge of https://github.com/ilastik/ilastik/pull/1723 we should redo the images in the workflow docs to reflect those changes and also exchange the header of the page.

Stuff to consider:

• Page header
• Pixel Classification
• Object Classification
• Carving
• Tracking

also:

• header in twitter profile