Merge pull request #3 from inspiran/master

Billing refactoring
rename billEntity() add executebillingRequest() to BillingManager
Rename createBillingRequest() to generateBillingRequest
Rename CreateBillingRequest to generateBillingRequest
Created mongo mapping for Billing Agreement
Added mongo mappings for new properties
Merge pull request #8 from jcroll/master

[WIP] Refactor