Midway through a massive update, commiting because I probably should.

Now calculates DR levels, and also can handle very long audio files. Uses modern libav functions, and generates more accurate WavePlots at the start and end of the audio file.
Removed all old code. Switch from OO approach to function-based approach.

WP Imager now only generates data for the WP itself. The server will generate thumbnails and previews automatically from this data. DR Levels now work for very short tracks too - the max peak is used instead of second max if there are less than 3 peaks.