Allow aliases for DBS URLs.

Allow aliases 'phys03' and 'global' for parameter Data.dbsUrl. They translate to:
'phys03': 'https://cmsweb.cern.ch/dbs/prod/phys03/DBSReader'
'global': 'https://cmsweb.cern.ch/dbs/prod/global/DBSReader'
Allow alias 'phys03' for parameter Data.publishDbsUrl. It translates to: 
'phys03': 'https://cmsweb.cern.ch/dbs/prod/phys03/DBSWriter'
Also, allow to specify the DBS URLs with trailing '/'.