Implement global parameters

[henhuy]

We need access to global parameters (i.e. WACC) in Adapter class.
Global parameters could be defined from outside via JSON or CSV.
We have to function to Adapter class which can get global parameter data.

[SabineHaas]

Check whether WACC is used for discounting.

Or directly implement discounting for multi-period optimiziation.
see oemof/oemof-solph#993 and oemof/oemof-tabular#163