Functions to copy data from a source folder to the data folder

[chellings]

analysis_toolbox: added functions fetch_data and fetch_data_in_range to copy data from a source folder to the data folder.

Useful to analyze data from the setup on a local notebook with a separate data folder.

Inviting @nathlacroix to review FYI @antsr @stephlazar

[nathlacroix]

Very nice feature @chellings . Initially, I wanted to add some functionalities which I had in my local version of this function but when trying to implement them, I realized it would be intricate due to the chosen structure of the "auto_fetch" feature throughout the module (resulted in some infinite recursive calls in edge cases which would be possible to manage but that would not be very robust to further changes). I therefore suggested only minor renaming changes:

• fetch_data --> copy_data: I believe this is closer to what it is doing as it could in principle copy to any location, not only locally (we could have an automated script calling this function once a month to copy data to the backup folder on Q, for instance)
• folder --> target_dir: I understand your logic of keeping the name "folder" for the target directory as it is the name used in the rest of the analysis_toolbox, but I do believe that the contrast "source_dir/target_dir" is clearer than "source_dir/folder" in the scope of a copy function and I think local code clarity should have priority over module-wide consistency, especially in the case of such a generic name ("folder" could be anything :p). Sorry for the long response time before the review. If you agree with these small changes, the pull request can be merged in my opinion.