This commit also enforces the interdiction of empty strings being
bound as string database parameters.  Either a non-empty string is
bound or no value at all is bound (nullopt).

Added the new disk instance field for storage class, requester, requester group, archive route to the frontend

Renamed drData (and its fields) to diskFileInfo to better reflect the use that we make of that structure

Added comments in the EOS interface doc.\nRenamed MountGroup into MountPolicy and removed MountPolicy (adapted SQL code).\nRemoved amount of data to warrant a mount from LogicalLibrary.

Changed the documentation fro the eos interface and the instance crosstalk, renamed User into Requester, refactored all the SQLITE code to have a GROUPNAME column in the requester, changed the tests

Changed the interface to EOS doc and changed the type of the first parameter of catalogue.getArchiveFiles from uint64_t to string