[ADD] account: add charge notes

[umiphos]

Description of the issue/feature this PR addresses:

A charge note is made when you need to add a charge to a transaction after an agreement has been broken.

In Peru, we use charge notes in order to create an special charge for the other partner to pay for extra costs from a service/product sale. Usually, in other countries you create another invoice, but in peru it's recommended to create debit note when you need to charge extra to a user.

With this change we add this way, it's just an addition to the credit wizard.

Examples

You give a discount to a customer and both agree that the payment is due to the 15 of the following month. The customer pays the 18 of the following month. You can create a charge note for the amount in the discount.

The customer gives you a check. One of your employees go to the bank to cash the check but the account of the check has no money in it. You can debit the amount of the total of the check plus a fee for the expenses of the service.

You are selling big furniture, the client agrees that only will be delivered to the doorstep. Once you arrive the customer needs your crew to place the furniture inside the house an that job takes several hours(or not but its extra work). You can charge this extra cost to the customer.

Note that most of this cases can be solved if we applied another invoice for the cost, but in some countries of LATAM we can do this document or even in some examples where the goods aren't billable we need to make this document.

Current behavior before PR:

We don't have a charge note

Desired behavior after PR is merged:

We will have a charge note

-- I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

[umiphos]

@nhomar this is the idea for debit note that we have in odoo-peru plus the idea you gave me about the boolean field in account.invoice to signal if is a debit note.

Next TODO: Make this work with odoo-peru

[umiphos]

@umiphos it's working with odoo-peru, but we can't make runbot work...maybe we need to configure the gitlab-ci file or travis...

[umiphos]

@luistorresm we are going to make a proposal to make debit notes part of the core, what do you think about this change?

[nhomar]

Please this MR will stay just for historic reasons.

Do it in master.

[nhomar]

I like the end solution BTW.