FELIX-4419 Open access to InstanceDeclaration and TypeDeclaration

* Added DeclarationBuilderService interface
* InstanceBuilder produces DeclarationHandle to XYZDeclaration
* Declarations now also implements DeclarationHandle
* Added some core-it tests to show typical service usage

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1571275 13f79535-47bb-0310-9956-ffa450edef68