Move paragraph back to developer doc and add cross-references

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Use PersistentEventLogLoader.v2.current_id as the defaut

- Move the discussion on configuration key change as a note
- Add commit extlink to point at the relevant modification revision

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)