dataMgr:importerParser/whImporter: support append records from dir

1) Add support to append all records files matching datatables in
   database stored in a directory using option '-m' combined with
   '-d'.
2) Add appendRecordsFromDir() in whImporter to append records from
   a directory.
3) Rename appendRecordsOnly() to appendRecordsFromFile().

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>