Use same format for str of proteus record

In trytond, we user , as __str__ for an instance and as value of reference field.
I think it will be easier to write code if proteus used the same format.

assigned to @ced

added proteus type::feature + 1 deleted label

added 1 deleted label and removed 1 deleted label

review291081002 updated at https://codereview.tryton.org/291081002/#ps282941003

New changeset 74a6b2213993 by Cédric Krier in branch 'default':
Use same __str__ as trytond instances
https://hg.tryton.org/proteus/rev/74a6b2213993

added 1 deleted label and removed 1 deleted label

closed

New changeset 804ec1bc7c04 by Cédric Krier in branch 'default':
Use same __str__ as trytond instances
https://hg.tryton.org/tryton-env/rev/804ec1bc7c04