Merge pull request #49 from inspiran/refactor

Refactor
pass global Elements and related fixes
Merge pull request #50 from WriteOrRead/refactor

pass global Elements and related fixes
start refactoring of pricing set processed values and properties
add attribute methods to product
updates to pricing set code
Merge pull request #51 from WriteOrRead/refactor

PricingSet changes
rename PricingElementValueInterface
updating elements
Merge pull request #52 from WriteOrRead/refactor

updating elements
Added basic fields to the billing request entity
* Added tracking of consumption data (eg. bandwith consumed)
* Added billing period start & end
* Adjusted billing agreement fields
* Added fiscal year & invoice type to Invoice
* Added an InvoiceItem interface