[MERGE] reports: make it possible to use only XML declaration, even with custom parsers.

[MERGE] reports: make it possible to use only XML declaration, even with custom parsers.

This makes report registration more uniform, and report rendering be possible
through the ORM (and thus the model service, instead of the report service).

To register a report, always use the database, i.e. a <report> tag within an
XML file. The custom parser, if any, will be specified in the database.
Previously specify a custom parser, the report was declared in Python.

Each model exposes a print_report() method, which will take the report name (as
many report can be defined on a single model) in argument.

bzr revid: vmt@openerp.com-20130327161129-6e7jz7l3lx7z1t18