Several additions and optimizations

NEW: Graphs - added CurveGraph class to draw non-stacked lines with markers
NEW: Graphs - allow graphs with negative Y values
CHANGE: FileCatalog/FC_scaling_test - automated sweeping of test parameters
NEW: FileCatalog - methods returning replicas provide also SE definitions instead of PFNs to construct PFNs on the client side
NEW:  FileCatalog - added getReplicasByMetadata() interface
CHANGE: FileCatalog - optimized getDirectoryReplicas()
CHANGE: FileCatalogClient - treat the reduced output from various service queries restoring LFNs and PFNs on the fly 
NEW: FileCatalog - LFNPFNConvention flag can be None, Weak or Strong to facilitate compatibility with LFC data 
NEW: added SSHOARComputingElement class