Add missing figures

[guillep]

Try fixing the mutalk chapter

I managed to build it in my machine with these missing files doing:

pillar build pdf Chapters/Mutalk/Mutalk.md
pillar build pdf index.md

Looks however that there are some broken refs

warning  (pdf backend): unreferenced destination with name 'Evaluation-of-mutan
ts'

warning  (pdf backend): unreferenced destination with name 'Mutant-generation'

warning  (pdf backend): unreferenced destination with name 'Coverage-analysis'

warning  (pdf backend): unreferenced destination with name 'Initial-test-run'

[Ducasse]

I will apply also some checkers on the book to see if they work. But I will do that with the special version of pharo. Just pushing some changes if I find some 'bugs.'