[IMP] allow many2many to specify formview (web client)

One2Many fields can specify sub tree and sub form view, to be used when
displaying a list view and when adding/editing an element.  Many2many
can display a sub tree view, but ignore sub formviews.  This can be
fixed by specifying an alternative_form_view to the popup form widget.
[IMP] account: account.statement.operation.template model
- better many2one ondelete strategies
- added analytic account domain
- added multi-company support
[FIX][TEST] membership: fixed tests. It is now clear that
tests crash and that there is a mismatch between the tests and
the module. However as the tests were badly written the asserts
did not fire.

Now the tests crash as they should be doing since a long time.
[FIX] membership: some fixes to try to make the tests pass.
[ADD] [TESTS] membership: added tests