DFC use for LFC data

[atsareg]

The LFC information can be stored in a non-DIRAC way in the SEs that are not in the DIRAC CS. Still if this information is added to DFC, we can try to cope with it. The SE
in this case will be the host name of the PFN added. If the LFN/PFN convention is preserved, then the PFN prefix in front of the LFN can be stored in FC_StorageElements in a special SEPrefix field. This field can be used as an alternative definition of the SE until it is properly defined.

The LFN/PFN convention configuration flag can be:
Strong - adding non-conventional PFNs is not allowed, PFNs are not stored
Weak - non-conventional PFNs are stored, but conventional are not