[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
[ADD] website_forum: Adding reporting functionality for Forum Questions and Answers.
[FIX] website_forum: Solving bugs of computed fields of forum.post