[IMP] crm: usability improvements

Among various small fixes, some changes :
- correct computation of default sales team, located in sales_team with a
small code cleaning. Rely on this method everywhere it is necessary.
- add a configuration option to enable the use of leads in sales team;
otherwise it is hidden
- better display of alias in empty list help;
- add a menu for next activities, that are the opportunities with an action
whose deadline is near assigned to the current user;
- automatic update of aliases configuration on sales team, based on whether
they use leads and/or opportunities;
- add a wizard to log the lost reasong when deactivating a lead or an
opportunity