Changed de Offering class in order to remove the need for timestamps in
the URIs.
Solved issue with prefixes when an empty LinkedUSDLModel was created.
Created source folder for unit tests code.
Added Duplicate URI Validation and Unit test.
Added Linked USDL Model validation capability.
Added exception and error message treatment for the entire API
Improved functionality in Offering and Service classes
Added unitary tests for validation algorithms
Added PricePlan and PriceComponent validations
Restructured Offering, Service, PricePlan, PriceComponent and PriceSpec
Added new Unit test for validations
Finished major model revision.
Finished model validation capability
Merge remote-tracking branch 'origin/Validations_dev'

Conflicts:
	SPIN_API/.classpath
	SPIN_API/src/usdl/servicemodel/CloudProvider.java
	SPIN_API/src/usdl/servicemodel/LinkedUSDLModel.java
	SPIN_API/src/usdl/servicemodel/Offering.java
	SPIN_API/src/usdl/servicemodel/PriceComponent.java
	SPIN_API/src/usdl/servicemodel/PriceFunction.java
	SPIN_API/src/usdl/servicemodel/PricePlan.java
	SPIN_API/src/usdl/servicemodel/PriceSpec.java
	SPIN_API/src/usdl/servicemodel/QualitativeValue.java
	SPIN_API/src/usdl/servicemodel/QuantitativeValue.java
	SPIN_API/src/usdl/servicemodel/Service.java