Wrong start/end/duration times when switching regions.

[julj]

When switching from one region to another one, the start/end/duration times are wrong. I guess this is due to the following lines

https://github.com/CrowdCurio/audio-annotator/blob/02e87176270f80a843c12ba78b958863adb4fccd/static/js/src/wavesurfer.regions.js#L206-L208

during which the regions are not swapped (in swapRegion) until the end.