Replace "for position only" (FPO) images

[geealbers]

There are twelve of them as of this writing:

• [x] fig-2--fpo.jpg
• [x] fig-2-11--fpo.jpg
• [ ] fig-3--fpo.jpg
• [x] fig-3-6--fpo.jpg
• [x] fig-6-4--fpo.jpg
• [ ] fig-8-8--fpo.jpg
• [ ] fig-9-11--fpo.jpg <-- being redrawn
• [ ] fig-10-13--fpo.jpg <-- being redrawn
• [ ] fig-11-5--fpo.jpg <-- being redrawn
• [ ] fig-15-5--fpo.jpg
• [ ] fig-19-5--fpo.jpg

[geealbers]

3.6 is on the server but not integrated yet