CS-1: Register a customer

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As a user, I want to register a customer into the system, so it can be set as sender or recipient on any invoice.

To do that, the user must specify at least the name and the Spanish TIN (Tax Identification Number, which is unique and represents the NIF or NIE for people and the CIF for companies). Optionally, you can add the address, the city, the province, the ZIP code (which can be only numeric) and the IBAN. Finally, an autogenerated code will be added to that registered customer, so it is identified across the system. However, you have the option to set it manually.

This process will be done through an UI which will show an form to introduce all the mentioned data previously.