Add a note clarifying that init-db is technically porcelain
Replace text in blob/tree/commit slides with images

Images provided by Yoshitaka Okubo.  Moved the text I had previously
written into notes; I'll explain that with reference to the images,
rather than having it written on the slides...
Adjust spacing
Japanese correction
Add slide for refs/branches/tags
Updated images from Dave
Remove rotation from 'Ref' header
Add Dave's name to title as he did the diagrams