Add support for secondary Finvoice intermediator address

[aksl]

Add support for specifying secondary intermediator address for invoices sent to bank network. When sending to bank network, the intermediator address should be specified in text format (like DABAFIHH), but when outside bank network, it should be specified in numeric format (like 003721291126).

Details:

• http://support.maventa.com/hc/fi/articles/213420585-Kuinka-l%C3%A4het%C3%A4n-laskuja-pankkiverkkoon-ja-vastaanotan-niit%C3%A4-sielt%C3%A4-

Suggestion:

• Add field to company
• Add binary field to client that specifies if secondary intermediator address should be used

[emaijala]

Isn't that for receiving invoices from bank networks? According to the linked page the intermediator is not mandatory when sending to the bank network. Or did I completely misread it?

[aksl]

Not sure if it's common, but it applies at Maventa atleast. Couldn't send an invoice before changed temporarily to the textual id.

[emaijala]

Related to #11, the selection could perhaps be based on the client type.

[aksl]

Will not work: in our case, a company has been using bank network address.

One (complex?) solution would be to add a list of sender addresses, make one primary (default), and then have an option to use any of the addresses for any client.