FIDMappers should be configurable

In DataStores derived from JDBCDataStore, and probably in all others as well,
there is a default of false for returnFIDColumnsAsAttributes() for all FIDMappers.
This should instead be configurable, so that one can decide upon it.
I know that with an explicit cast to JDBCDataStore you can call setFIDMapper()
and change this behaviour, but this is cumborsome and also it's not applicable
to all DataStores.
But the real bad thing is that it's not usable from GeoServer, since it's not usable
from the DataStoreFactory.
In my opinion ALL parameters should be accessible through the DataStoreFactory,
there should never be any case where one must configure a DataStore with using
its DataStoreFactory.