Impacted versions: Master - probably all

Steps to reproduce:
Go to Settings Screen

Current behavior:
You'll see Authentification written twice.  In English, and especially in English technology speak the usual word is Authentication.

The only real issue it causes is that when searching for docs, you would search for Authentication (e.g. "How do I setup Oauth Authentication with provider x?"

Expected behavior:

Video/Screenshot link (optional):
![image](https://user-images.githubusercontent.com/5093264/29589757-99092af0-87ea-11e7-8bbe-dd8593b54d42.png)

Seems it occurs 4 times in code, but didn't want to PR as I don't understand translations
![image](https://user-images.githubusercontent.com/5093264/29589851-1e30f71c-87eb-11e7-94a7-fdb16a9eeccf.png)

FIx if you want, close if you want, I won't be offended and can manage


addons/base_setup/models/res_config_settings.py
from odoo import api, fields, models, _
class ResConfigSettings(models.TransientModel):
    _inherit = 'res.config.settings'
    group_multi_company = fields.Boolean("Manage multiple companies", implied_group='base.group_multi_company')
    company_id = fields.Many2one('res.company', string='Company', required=True,
        default=lambda self: self.env.user.company_id)
    default_user_rights = fields.Boolean("Default Access Rights")
    default_external_email_server = fields.Boolean("External Email Servers")
    module_base_import = fields.Boolean("Allow users to import data from CSV/XLS/XLSX/ODS files")
    module_google_calendar = fields.Boolean(
        string='Allow the users to synchronize their calendar  with Google Calendar')
    module_google_drive = fields.Boolean("Attach Google documents to any record")
    module_google_spreadsheet = fields.Boolean("Google Spreadsheet")
    module_auth_oauth = fields.Boolean("Use external authentication providers (OAuth)")
    module_auth_ldap = fields.Boolean("LDAP Authentification")
    module_base_gengo = fields.Boolean("Translate Your Website with Gengo")