1) Fixed typo in BillyServiceError
2) Changed auditevent to audit_event
3) Fixes in coupons models:
	-Import order
	-guid added on top of id
	-marketplace -> group
	-coupon_id -> external_id
4) Added Groups model
5) Added uuid factor from balanced_services
Update invoice sand coupon models.
Styling fixes in customer model.
1) Updated invoices to have includes_trial parameter
2) Customer object can trial method
3) Customer object current_debt method
4) Custoemr object is_debtor method
Customer and Invoice models looking beast.
payouts model looks pimp. Moving to plans object
Plan model looks sexy. Moving on.
1) Fixed group_id foreign key in a bunch of places
2) Outlined transaction models
3) Modified customer class to include
-currentdebt method
-sum_plan_debt method
-clear plan deb (todo)
Updated transactions method.
Too much shit to comment on.
Am Commit. Made cleaning on models. Plans model cleaned.
Coupon models updated.
Fixed payouts model
Customer model fixed, which wraps up top tier models.
Fixed model keys again.
Improving models, fixing imports.
Fixedi mport loop issues which meant some of the names had to be hardcoded.
Models fixed to a creatable state. Moving to remove unecessary inspections.
Smarter models.
Added retry intervals to the plan debt methods.