[fill_missing_daybefore] fills with day before arange period, not with day before gap

[cdemulde]

No description provided.

[cdemulde]

This function needs to be adjusted quite a bit: the arange argument will have to show in what period to replace/fill values, and the function will have to detect what actual gaps it can fill, based on the range_to_replace argument. It can then make use of the data of the day before those actual gaps.