[FIX] paydays: Show payment_days label
[FIX] some PEP8
[FIX] all PEP8
[FIX] pylint
[FIX] No module named mx.DateTime
Merge pull request #11 from eLBati/fix_pep8_7

[FIX] pep8
[add] account_vat_on_payment - copied from
https://code.launchpad.net/~domsense/domsense-agilebg-addons/6.1
[imp] headers
[imp] first porting changes
[fix] handling foreign currency for additional move lines
[FIX] using right journal in context
[IMP] line lenght
[imp] using esplicit dates
[IMP] some PEP8
[imp] other PEP8
[imp] other PEP8
[fix] URL
[FIX] typo
[ADD] avoid including write-off if set in voucher.
                                That means: use the invoice's total
                                (as we are in 'full reconcile' case)
Added a selection field to define a default value for VAT on Payment flag.

Usually, invoices emitted for a particular customer/supplier have the
same value for the VAT on Payment flag.
This patch adds the possibility to specify the default value of such a
flag.
This definition must be done inside the partner form and is made through
a selection. This is done to force the user to flag the right value.
Using a boolean is too easy to forget to check the field.
Once the default value is set, all subsequent invoices created for that
partner have the VAT on Payment flag automatically set to the right value.