20121209
========

Started to work on :mod:`lino.modlib.finan`.

There should be a more or less hard-coded account type 
`accounts.utils.BankAccounts` which is used as filter 
for the choices to be displaied in Journal.account.

`UserLevels` (which I'm going to rename to `UserRoles` one day) and 
`AccountTypes` are examples of choicelists where inheritance 
can be useful.
But to make it possible, we first need to get rid of the required choicelist in the `__init__`.

Updated the docstring of :mod:`lino.core.choicelists` which didn't pass the doctest.