Improve visibility changes as specified in the task

Hi, Following Changes is done in the branch:
- In Invoce wizard of Quotations/Sales Orders:
- Change tooltip of fixed price + percentage field.
- Change tooltip of 'What do you want to invoice' field.
- Put blocking alert for customer and products in sale_order,purchase_order,invoice,product and picking.
- To Renew button also search by End Date and Prepaid Service Units fields in searchview of contract to renew menu.
- Warning message on partner in sales order, purchase order, invoices. 

Thanks.