Stochastics, timeline aggregation, excel import scenario fixes

[ArttuTupala]

REPLACED period_share_of_year with complete_period_share_of_year for obj_function, has caused issues with stochastics, inter-period rolling and nodal_price. Fix timeline aggregation for timeseries without all timesteps (eq. storage_reference_value) Only aggregate once per roll patch. Excel import scenario fixed after broken with 0.8