[FIX] account: chart of account opening period selection

If a special period is present, it must be selected fist
Fixes #3946
[FIX] stock: compute average price on action_done

The average price computation is now deduplicated and moved to
a separate function called in stock_move action_done.
This makes sure it is always called when a stock.move is
processed, even without going through the partial picking wizard.

Fixes #2991
Closes #3949
OPW-615491
[ADD] purchase: average price computation test
[IMP] mrp: add prepare method for manufacturing orders to allow override

Fixes #3973
[IMP] web: do not fully hide pager in grouped view

When the list view is grouped, the page count should be hidden as irrelevant.
However if it's fully hidden, the limit can no longer be changed.
Instead of hidding the pager, this commit hides the arrows and replaces
the content by the current limit to allow to be changed.
[FIX] product: add store=dict to field name_template

Recompute the name_template field if the template changes.

backport of 41628fc + f25c5d8 to 7.0 plus some optimisations in triggers
Fixes #3277
[MERGE] forward port of branch 7.0 up to d6daf5f
[FIX] purchase: do not use deprecated api
[MERGE] forward port of branch 8.0 up to 31a01ea
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32