better integration with pandas dataframe

- use of DF column labels
- remove lines with no-data's and flag column
- stations_order calls stations_list
- numpy.nanvar instead of numpy.var
nanvar

fixme: numpy statistics consider nan's
nanvar replaced var
ddof = 1 for sample variance
code clean, add return to gsimcli and run_par

- removed stcol and varcol dependences
- gsimcli now returns homogenized path, st order, detect and fill
numbers
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small fixes (header, nanvar)
pandas adapt, merge_output, bug fixes, code clean

- detect: remove flagcol, then append again; count nodatas and missing
- fill_stations: return list of int's
- take_candidate: adapted to pandas, fixed flag issues, fixed save
- station_order: fixed variance method
- save_output: adapted to pandas
- merge_output: new func to merge batch decade' results and add a
summary