MDL-46455 core: added backup log store interface
MDL-46455 tool_log: added function to return stores that support logging
MDL-46455 tool_log: added backup helper
MDL-46455 core_backup: use log stores to perform the backup
MDL-46455 logstore_*: added backup support
MDL-46455 core_backup: use log stores to perform the restore
MDL-46455 logstore_*: added restore support