Can emit invoice to backoffice

[thenrio]

backoffice is xero

Given Nick belongs to company WineAndFood
And Nick as invoice with 5 places at 220, 3 diner at 40 and 2 places at 270 for user 'nicolas'
Whent app emits invoice to xero
Then there should be a xero invoice for customer Pierre of WineAndFood with amount 1760
And xero invoice should have 3 lines

[thenrio]

implemented with resque job (0da75c2)