Several fixes for tools

Several improvements for the Condition DB command line tools:
- conddb_import:   support look up of TAG_MIGRATION table to remap tag from V1 to V2 DB
- conddb_copy_iov: same as for import
- conddb_migrate: look up into the POPCON LOG, to extract the insertion time to be propagated in the V2 DB.

Packages involved:
CondCore/CondDB
CondCore/Utilities