Rename Node to Device, Repository to Folder (fixes #739)

I am pretty sure we could make the rename throughout the code too quite easily with some `sed` magic, if we wish. (Config migration...)
I usually don't like inconsistencies between code and UI.

Furthermore, the console still says Node/Repo everywhere, not sure if we want to rename it there as non-technical people probably don't poke with that, and t's a halfway house one way or another.