[ADD] custom_pos: customized pos to handle custom price and min price

[vpan-odoo]

Steps to reproduce:

• Install custom_pos module (depends on point_of_sale).
• Open Point of Sale > Products > Products > Select any product.
• On selecting any product the product template form will appear.
• Set the custom price (this price will be considered in the order line) and min price field(below this price salesman cannot sell).
• Open pos register in which the product we edited is there.
• Select the product.
• In the order line you're able to see the product bar code with the product name and strike through standard price with the custom price.
• Now try to enter the manual price which is lower than the min price field.
• It will pop up the Alert Box that you cannot sell the product below its min price also it will reset the unit price of the product to its custom or standard price.
• Click Payment > choose any payment method > validate it will open receipt press new order
• Click actions > Refund > Enter product bar code in the search bar and select Product Barcode
• It will filter all the orders which have particular product in it.

Purpose of Changes

• We have to display custom price along with the standard price to make the customer feel that he got some concession on purchasing the product.
• Also we have to restrict the salesman to sell the product below its minimum price
• We want to search the orders using the product barcode

Changes

• After this commit, we are able to see two new fields in the product template page i.e. custom_price and min_price.
• If the custom price is set, the pos order line will consider custom price as its price and we can see the strike through standard price and then custom price.
• Also we are able to see the product barcode before the product name in the orderline.
• If the user tries to set the product price (manually or by applying discount) below the min price it will pop up the alert dialog box and reset the unit price to its custom price if it is available, or its standard price.
• User can now able to search the orders using product barcode.

[robodoo]