Adapting single-recording download from player

[kdarras]

We will not use uncompressed audio for storage anymore (#389 ), so there should only be two buttons for downloading the current view's recordings from the spectrogram player:

• "download lossy file" (MP3 for <44.1kHz sampling rate, OGG for >44.1kHz)
• "download lossless file" (FLAC)

This should work both for the original recordings (when not zoomed in) and portions of it (when zoomed in).

If a new file is generated (i.e., when zoomed in or when choosing lossy downlaod from a lossless original file) metadata (ID3, Vorbis tags...) should be added to the downloaded file.