[ADD] module base_partner_helper

The purpose of this module is to gather generic partner methods in the same module.
It avoid to grow up excessively the number of module in Odoo for small features

Validation is done in launchpad:
https://code.launchpad.net/~akretion-team/partner-contact-management/7.0-partner-helper-dbl/+merge/221501

Still `module` is in singular, while it must be in plural. Sorry to insist...