Bug 52350: Allow sections to be indented and outdented

This updates the schema so it can record the indentation position,
and also adds x-positioning to the sortable sections. Sections can
be indented up to five levels.
Change-Id: Ide9a63b09209887b5cdc35b016a1b29e7e012525
Merge "Bug 52350: Allow sections to be indented and outdented"