Added Statistics Schema + CppSchemaStatementsReader to compare the statistics database against its schema

Queueing of Archive jobs now use the ContainerAlgorithms instead of the methods in the ArchiveQueue object
Created a base class (interface) that allows to add and remove object(s) from the ownership of an Agent (implementation : AgentWrapper) or from an AgentReference (implementation : AgentReference)

Started to queue the ArchiveRequest for Repack

Removed the "User" message from the cta.proto (duplication of UserIdentity message)

Moved the getPoppingElementsCandidates() method from RetrieveQueueFailedAlgorithms, RetrieveQueueToTransferAlgorithms and RetrieveQueueToReportToRepackForSuccessAlgorithms into RetrieveQueueAlgorithms
This removed the duplication of the code in this method repeated 3 times

The getNextSucceededRetrieveRequestForRepackBatch is implemented and integrated in the expandRepackRequest test

Each thread has its own rados context. The thead pool, when used will allow better
parallelism of asynchronous requests.

This required some rework on the backend creations as the threads will need logging.

New URLs are rados://user@pool and file:///tmp/XXXXX. Otherwise, we fall back to interpreting
the URL as a bare path.

Implemented unit tests for storage classes and archive routes.

License comment is no longer filtered out by doxygen when generating web pages of the individual source files.