Pyerrors backlog

With this tool, we aim at making it easy to backlog correlation functions that can be read with pyerrors. This is done in a reproducible way using datalad. In principle, a dataset is created, that is automatically administered by the backlogger, in which data from differnt projects are held together. Everything is catalogued by a searchable SQL database, which holds the paths to the respective measurements. The original projects can be linked to the dataset and the data may be imported using wrapper functions around the read methonds of pyerrors.