pep8
striped down new/edit section forms
fix section delete ret_url
count deleted sections for new section postfix

The idea to append the number of existing sections to each new
sectiontitle had a serious flaw considering one can delete
sections.

I fixed this be counting children instead of subpages.
As far as I understand the subpages are all children which
have not been deleted.
Merge pull request #576 from xi/feature-add-section-form

add section form