Merge pull request #67 from inspiran/master

Updated billing agreement to include initial billing date & billed-to date
add PayPalExpressRecurring
add dateFromOffset() and start computeNextCycle()
Removed taxonomy enities from core
added vespolina taxonomy as dependency
Merge pull request #71 from jcroll/master

[WIP] Remove Taxonomy entity and add it as dependency
Update CartInterface to extend OrderInterface
adjust offset calculation to only adjust month and year offsets
remove unneeded code
Created new properties for BillingAgreement
created getters and setters for new properties
Added docblocks
Added invalid argument exceptions
Changed setter/getter name
Renamed getters and setters for setting paymentProfile
Merge pull request #72 from jcroll/master

[WIP] Refactoring
Update Taxonomy interface name
Update Taxonomy interface name
* Allow an order to be attached to a (sales) channel
* Fixed and dropped some deprecated tests