Disable states for prev and next.
Prev is disabled when the start second is 0.
Next is disabled when the end second is within the minimum of the end of the audio recording.
Added minimum duration to show in the configuration file.
Changed the next URL so that the end point will not go past the duration of the audio. E.g. if the audio is 100 seconds and the current page is 60-90, the next button url will be to 90-100 (10 seconds long).