Added dbtk_excel.py, to remove dependency on xlrd for scripts that don't use Excel.
Added dbtk_excel.py, to remove dependency on xlrd for scripts that don't use Excel.

goelakash/retriever,davharris/retriever,bendmorris/retriever,bendmorris/retriever,goelakash/retriever,davharris/retriever,bendmorris/retriever,henrykironde/deletedret,henrykironde/deletedret,embaldridge/retriever,embaldridge/retriever,davharris/retriever,embaldridge/retriever