Try and improve auto-follow behavior on certain models

All models (tables) have auto-follow behavior, i.e. customers linked to the object become automatic followers. 
However, for more internal models like projects, taks, invoices, etc. this may not be the desired standard behavior, as we wish to avoid to accidentally involve the customer there.
On the other hand, with other models (e.g. helpdesk tickets) we would like to add more people perhaps.