Documentation of the public methods of the sorter

Harmonized the copyNb type to uint32_t
Corrected a bug in RetrieveQueue::getContainerSummary() --> After insertion in the queue, the number of files and bytes added were equal to 0.

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)

Queueing of Archive Jobs is done and unit tested
Queueing of Retrieve Requests is not completely done yet

Conflicts:
	scheduler/OStoreDB/OStoreDB.hpp
	scheduler/OStoreDB/OStoreDBFactory.hpp
	scheduler/OStoreDB/QueueItor.cpp
	scheduler/Scheduler.cpp

CatalogueTest now asserts new archive file identifiers are unique as opposed to strictly incrementing sequentially by 1

Woah!  Got carried away with const.  This commit Removes the const
qualifier from the ArchiveFileItor::next() method because next()
modifies the iterator.

To loop through an ArchiveFileItor:

  auto itor = catalogue.getArchiveFilesForRepackItor(vid, startFSeq);
  while(itor.hasMore()) {
    const auto archiveFile = itor.next();
    // Do something with archiveFile
  }

Started to queue the ArchiveRequest for Repack

Conflicts:
	objectstore/Agent.cpp
	objectstore/RetrieveQueueFailedAlgorithms.cpp
	objectstore/RetrieveQueueToReportAlgorithms.cpp
	objectstore/RetrieveRequest.cpp
	scheduler/OStoreDB/OStoreDB.cpp
	scheduler/OStoreDB/OStoreDB.hpp
	scheduler/OStoreDB/OStoreDBFactory.hpp
	scheduler/OStoreDB/QueueItor.cpp
	scheduler/RetrieveMount.cpp
	scheduler/Scheduler.cpp
	scheduler/SchedulerDatabase.hpp
	xroot_plugins/XrdCtaArchiveFileLs.hpp
	xroot_plugins/XrdCtaListPendingQueue.hpp
	xroot_plugins/XrdCtaTapePoolLs.hpp

It was using vid as container identifier where it should have used
tapepool.

Changed 'catch (cta::exception::Exception ex)' to 'catch (cta::exception::Exception &ex)' in order to avoid error: catching polymorphic type ‘class cta::exception::Exception’

Changed 'catch (cta::exception::Exception ex)' to 'catch (cta::exception::Exception &ex)' in order to avoid error: catching polymorphic type ‘class cta::exception::Exception’ by value

Changed 'catch (exception::Exception ex)' to 'catch (exception::Exception &ex)' in order to avoid error: catching polymorphic type ‘class cta::exception::Exception’ by value

Changed 'catch (std::out_of_range)' to 'catch (std::out_of_range&)' in order to avoid the error: catching polymorphic type ‘class std::out_of_range’ by value

dedicated PV for quarkdb

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

Simplified protobuf schema.

Previously these were references, but sometimes we want only an archive
queue itor or only a retrieve queue itor. Now we can set the unused
itors to nullptr.