Refactor resource calendar and resource mixin:
- add a required timezone field on models 'resource.calendar' and 'resource.resource';
- resource calendar attendances are now computed in the timezone of the resource
or the calendar;
- improve API of 'resource.calendar' and 'resource.mixin';
- avoid other modules from using the implementation methods of 'resource.calendar';
- refactor implementation of 'resource.calendar' to make it more efficient.
Raphael Collet
975c6c8639