loading data from other folders

Extra-data allows loading data from a list of additional folders using the 'data' argument:

• tb.load use subFolder instead of data, maybe we should be consistent with extra-data and use data as argument
• subFolder can only be a string so that the completed folder path can be saved as argument. This is too limiting for data that are in 'raw', 'proc', and other folders for data retrieved from influxdb. It used to be that proc contained all of raw so data could be loaded from a single folder but this is not the case anymore as proc contains only processed data and nothing else to avoid duplicating data. Also, we retreive data from influxdb quite regularly now.