Improve party required usage
Setting party required on an account does not always work because it is not always possible to determine a party. Our initial thought was that user will set it only on meaningful account like receivable or payable. But it happens that people miss-used it [1] because it is not clear when this option can be used.
I think we should find a way to have a nicer way to deal with it. For now, the error is raised at the run time when a document tries to create a move.
* One solution would be to add a domain on the account fields which can not be party required. But this will create astonishment to the user who will not understand why he can not select a specific account.
* We could limit it to some balance type from #4990 (closed), but this will prevent to have this feature for income accounts. (Even if for now it does not work because the deferral wizard does not care about party required).
* Also we could use the company party for all the cases where the party can not be derived from the document (like counter part of the statement). But this solution will not feed the system with new information.
* We could try to always have a value for party required. The example of the counter part of statement could be to request to have a party on the journal statement, etc. This will require to analyze all the move creation.
[1] https://groups.google.com/forum/#!topic/tryton-fr/g6egcRj-w_M