Allow LineItem credits field to be null
Update LineItem model fields to not use '' as a default
Update billing statement tasks to include account fee
Fix billing statement view tests after adding account fee
Update the context given to billing statement template to use 'sections' instead of 'channels'
Ensure vumi is the last biller displayed on statements
Handle Nones in billing statement template
Change billing statement view tests to manually create statements
Don't add a billing statement line item for the account fee
Merge branch 'develop' into feature/issue-1071-add-account-fee-to-billing-statements
Avoid passing around from_date and to_date when generating billing statements
Fix mk_statement test helper to set the statement to_date to the end of the month
Avoid hardcoding 'Vumi' as the system biller name
Fix new billing settings to default to the appropriate global settings
Merge branch 'feature/issue-1071-add-account-fee-to-billing-statements' into develop
Merge branch 'develop' of github.com:praekelt/vumi-go into develop