Migration of account_credit_control

* Migration for version 8.0
 * Uses the new API
 * Updated test scenario (payment of invoices was done using bank statement + voucher, now only voucher)
 * Replaced the mako report ("webkit") by a QWeb one

The tests in this module are based on oerpscenario, precisely this branch which have some changes for odoo 8.0: https://github.com/camptocamp/oerpscenario/pull/17
The scenario are launched with the tag @base_finance, then @account_credit_control to test the module.
Travis won't be able to test them unfortunately, at least I run them successfully on my local computer.