Start concurrency tests. Add constraints to GenericInvoice
Start concurrency tests. Add constraints to GenericInvoice
Start test fix
Merge branch 'concurrency-fix' of github.com:premium-minds/billy into concurrency-fix

Conflicts:
	billy-portugal/src/test/java/com/premiumminds/billy/portugal/test/services/documents/TestConcurrentIssuing.java
	billy-portugal/src/test/java/com/premiumminds/billy/portugal/test/services/documents/TestDocumentIssuingService.java
	billy-portugal/src/test/java/com/premiumminds/billy/portugal/test/services/jpa/TestJPAPTBusiness.java
	billy-portugal/src/test/java/com/premiumminds/billy/portugal/test/util/ConcurrentTestUtil.java
Fix headers
Update concurrency test. Fix test structure.
Merge branch 'concurrency-fix' into develop