[ADD] [7.0] 'pos_order_pricelist_change' module

Add a "fix module" to manage correctly the changes of pricelist in a POS Order.
Without:
- when the user change the pricelist (or the customer), it's not possible to apply the new pricelist, and there isn't a warning to inform that there is a problem. (not as in Sale module).

With that module:
- There is the same warning as in 'sale' module, when the user realizes a quotation;
- There is a button to "recompute with pricelist" with pos order is in draft state;

Note:
- Flake8 OK;
- demo data updated;
- feature and non regression covered by python tests;