[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.
[ADD] account_analytic_analysis: Added a Contract stat button to display number of contracts and it leads to contract form view.[REM] account: Removed contract stat button.