Purpose of this commit is to always have a default calendar for each
company and ensure it is correctly set on resources.
Some cleaning is also performed in resource models to remove unused
fields, improve labels and make views a bit more odoo-ish.
* [REF] res_company: add a m2o to the default calendar to use in the
company as well as a o2m linking all resource calendars used in the
company. Some code has been added to correctly update existing
companies when installing the module;
* [REF] resource_calendar
* [REM] manager field on resource.calendar: this field is never used
and is not necessary anyway
* [ADD] global_leave_ids: filter leaves on a calendar to see global
company leaves
* [IMP] better default company / calendar computation to ensure there
is always a calendar attached to a resource
* [IMP] improve resource and calendar views in order to look more like
other odoo views
Thibault Delavallée