Sampleholder add tuple

I often get confused when passing all the arguments of
SampleHolder.add
as a string that's then evaluated.
This change allows to pass in filesCommand=(function, dictOfParameters)

I tested it with eos, and it works; if you agree with this change, we should define in 'sites' a function returning a dict with default parameters for the other storage commands (see supy.sites.eosPars).
Example usage:

exampleDict.add("sampleName",
                        (supy.utils.fileListFromEos,
                         dict(supy.sites.eosPars().items()
                              +{'location':"/eos/atlas/blah"
                                }.items())),
                        lumi = 1.0)
One bit that I don't like (but I couldn't come up with a better solution)
is to concatenate the dict of the default parameters with the ones in the analysis file:

dict( dict1.items() + dict2.items() )

Thanks,

davide