And improve compression of purchase
Based on https://docs.google.com/document/d/1X0kBpPsN1pkKyqKfX3JTXB7Tam2rgaYFkmHgV0TeP7Q/edit#
* by-application (odoo-wise) grouping * use part of the accounting TOC defined on pad * support for "internal" tocs & fixup front toc * various changes and improvements to extensions May be missing: inherited document banners?