[Feature] generalise downsampling script further, so it works on other species than tadpole

[alessandrofelder]

Is your feature request related to a problem? Please describe.

The downsampling script added in #26 is more general than the blackcap, but could be even more general going forward.

Describe the solution you'd like

• config for downsampling,
• generalise getting wavelength and sample id from folder name
• write logs to logs folder
• have just one root folder, and expect a sourcedata subfolder?