This MR adds a
GKFS_METADATA_MOD that can be used in a similar manner to
GKFS_DATA_MOD. It also adds a "MetadataModule" logger that can be used to emit messages from the internal code of
MetadataDB. This logger replaces the "MetadataDB" logger that was being instantiated in
daemon.cpp but not used.
Closes #161 (closed)