Implementation of the local caching of the OCDB set required some upgrade of the...

Implementation of the local caching of the OCDB set required some upgrade of the CDB access
framework

Main changes:

- Public method GetId(AliCDBId& query) added to AliCDBManager and AliCDBStorage. It is used to retrieve the Id of the valid object
without retieving the object itself.
- "Remote storage" added to AliCDBManager's possible storages. Remote storage is used if it
is activated and if object is not found in the default storage. This is used in case an
object in the local cache is lost before the job is executed.