Scribble manual: make "Images" section in ToC be useful

Remove the "Images" section for `scribble/manual`, add an "Images"
section for `scribble/base`.

As suggested by Shriram.
pkg/db: fix some missing table preparations
pkg/db: add support for grouping calls as a single transaction

Also avoids reundant table-preparation checks for calls that are
grouped together.
pkg catalog-update: install updates as a single transaction

Relevant to PR 14848