fix the excel reader: hours & header

in the excel.py there is a fix enabling reading xlsx files with both
datemodes: (see #4332)
in the parsers.py there is the fix for readinh the header even if there
are additional rows (to be skipped) between a header and the data (see: #4340)

I hope this PR is adequate. If not, please let me know.
I can supply the sample file for testing proving that it works. See also:
https://github.com/timmie/example_code_data