[ADD] create dav_calendar_sync addon

creates new addon dav_calendar_sync to synchronize caldav events on Odoo calendar

dav_calendar_sync/models/res_users.py

@@ -0,0 +1,7 @@
+from odoo import _, api, fields, models
+
+class Users(models.Model):
+    _inherit="res.users"
+
+    calendar_event_ids = fields.Many2many('dav.calendar', 'dav_calendar_event_user_rel', string='Dav Calendars Events')
+    calendar_todo_ids = fields.Many2many('dav.calendar', 'dav_calendar_todo_user_rel', string='Dav Calendars Todo')