Inherit core configuration variables

To avoid repeating ourselves, we will now inherit configuration
items from core.common.settings.local if they aren't redefined
in the local configuration.

Current list of inherited variables:
 - MY_SECRET_KEY
 - dbaccess
 - LOG_ROOT
 - defaultDatetimeFormat

Signed-off-by: Eygene Ryabinkin <rea@grid.kiae.ru>