cmfs-tools: add feature_string.c to libcmfs

Copy and modify ocfs2-tools/libocfs2/feature_string.c, add basic support
to feature string and bits.
cmfs-tools: add nojournal support to mkfs.cmfs

Currently cmfs-tools does not support jdb2 journal, after adding
feature_string.c to libcmfs, this patch add basic nojournal support to
mkfs.cmfs.

If user specifies "--fs-features=nojournal",
CMFS_FEATURE_COMPAT_HAS_JOURNAL will be cleared from super block flags.
So we can test kernel code ASAP without journal support.

This commit just passes gcc compiling now.