[crm] implementation planner

- Task: https://www.odoo.com/web/#id=8592&view_type=form&model=project.task&menu_id=3942&action=327
- Pad: https://pad.odoo.com/p/r.4BHh6hQdZ4GPR2qE
This many line in common in next_page, and onclick_menu. Create a new private function `_switch_page` with '#planner_pageID' as param (indicating the tpage to display).
So next_page and onclick_menu should extract and prepare the '#planner_pageID' and call _switch_page.