Migration of all python code, mostly withtout chagnes. And adapting
xml files to guidelines.
On calendar.py, some changes have been perform to make the migration works :
- `_compute` method has been split into `_compute_dates`, `_compute_attendee` and `_compute_display_time`.
- remove unused method `onchange_partner_ids`, `check_partners_email`
- make `compute_rule_string` use a cache record instead of a value
dict to avoid crashes
- remove `new_invitation_token` method, and make it a default value on attendee creation
- add a default value on `day` field, otherwise the "Please select a
proper day of the month" exception is raised during the onchange
Martin Trigaux