fstools: add the new fstools package

include/target.mk

package/base-files/files/etc/init.d/done

package/base-files/files/lib/preinit/80_mount_root

package/base-files/files/lib/upgrade/common.sh

package/network/services/mdnsd/Makefile

package/network/services/mdnsd/files/relay.hotplug

package/network/services/mdnsd/files/relay.init

package/system/fstools/Makefile

package/system/fstools/files/fstab.default

package/system/fstools/files/fstab.init

package/system/fstools/files/mount.hotplug

package/system/fstools/files/snapshot

package/system/ubox/Makefile