Xero integration

1. Enable Xero integration in General settings
2. Create AcadiaPOS in Xero dashboard, take contact ID from the URL and fill it as well

In Xero, go to Chart of Accounts and create an account called:
SYNC001
Type should be Revenue / Sales, and tax rate should match the one used in POS. 
Create an additional SYNC002/3/4 for each additional tax rate that needs mapping
Fill those codes in point of sale tax rates('Xero account' field)

Then create 
SYNC005/06/07..etc for each of the payment method that needs syncing(type CURRENT ASSET, click Allow payments to this account checkbox), and fill those codes in each payment methods in point of sale