config: consolidate CFG_UNSUPPORTED and CFG_ADVANCED settings

These settings are in the "unsupported" group:

devices/loopfiles
log/activate_file
metadata/disk_areas (section)
metadata/disk_areas/<disk_area> (section)
metadata/disk_areas/<disk_area>/size
metadata/disk_areas/<disk_area>/id

These settings are in the "advanced" group:

devices/dir
devices/scan
devices/types
global/proc
activation/missing_stripe_filler
activation/mlock_filter
metadata/pvmetadatacopies
metadata/pvmetadataignore
metadata/stripesize
metadata/dirs

Also, this patch causes the --ignoreunsupported and --ignoreadvanced
switches to be honoured for all config types (lvmconfig --type).

By default, the --type current and --type diff display unsupported
settings, the other types ignore them - this patch also introduces
--showunsupported switch for all these other types to display even
unsupported settings in their output if needed.

lib/config/config.h

@@ -198,6 +198,8 @@ struct cft_check_handle {
 	unsigned skip_if_checked:1;	/* skip the check if already done before - return last state */
 	unsigned suppress_messages:1;	/* suppress messages during the check if config item is found invalid */
 	unsigned check_diff:1;		/* check if the value used differs from default one */
+	unsigned ignoreadvanced:1;	/* do not include advnced configs */
+	unsigned ignoreunsupported:1;	/* do not include unsupported configs */
 	uint8_t status[CFG_COUNT];	/* flags for each configuration item - the result of the check */
 };