[ADD] dav_account: create addon to connect Odoo to a DAV server

Users can add several DAV servers to their profile preferences.

dav_account/models/res_users.py

@@ -0,0 +1,6 @@
+from odoo import _, api, fields, models
+
+class Users(models.Model):
+    _inherit="res.users"
+
+    dav_server_ids = fields.One2many('dav.server', 'user_id', string='Dav Server')