Analyzer enhancements

[bemain]

• Create dummy waveform for when a song is loading.
• Show the loop section on the waveform widget.
• Pin the last chord if no new chord has been played.
• Give Analyzer its own card.
• Detect key of song.
• Detect tempo and show beats on the Waveform widget.
• Implement syncing the metronome to the tempo of the song.