Saving sample metadata

[exa04]

Whenever a sample is downloaded, the only way to verify in-app is to check whether its name is the same as the one generated from the online resource. Basically, all of the metadata (author, date, etc.) is lost.

This might become a problem as, in the future, we could want to make downloaded samples from the LoopbaseContent/loops folder browseable. How about saving all this metadata to ~/.loopbase, a new hidden folder for this type of data (%APPDATA%/loopbase on Windows, etc)

[exa04]

This is related to section switching, so I'll postpone it to pre-3