[IMP] model: Improved read_group method to display empty column result an...

...d folded columns from related model and default_group_by field will be automatically added to the kanban no need to declare in kanban to enable the button 'Add a new column'. pass options in the read_group, In options pass 'fold_field' and 'display_empty_column' fields and remove _group_by_full methods from crm, hr_recruitment, project, project_issue, survey, website_event_track, website_forum_doc modules.

- Task: https://www.odoo.com/web?&debug=#id=7915&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.HUjKxbzyZdbgek0f
I think that to avoid having an "if ... else ..." behavior, we should instead have a default _group_by_full method called only if some options like display_empty_columns are set. Probably two default methods should be set
 - one for many2one-like columns, that perform a name_get (quite like you did just below) on a domain (currently your option in domain); by the way take into account that if a field fold exist, it should probably be used by the read_group (we love magic) even if fold_field is not set in the options
 - one for selection columns, that simply read the various key / value in the selection of the field