browserify package.
Refactored the `playFrom` method to use the new scheduling system.
Removed the `playPrev` method.
`playNext` will only play the next sequence as it is named.
Reworked the `playAll` and Scheduler to be more resilient.

- the scheduler now works with sequence objects
- several events are triggered: `playall.sequence`, `playall.postpone` and `playall.end`
- `getNext` now has an extra option to return a segment which end time overlaps with the reference value
Removed `getCurrentTime` wrapper.