Task for defining timestamps

[xavierfav]

Currently we propose only one type of annotation task (validate category annotations).
This validation task allows us to evaluate the presence of a sound category in an audio sample, but we have no knowledge about when exactly the type of sound occurs.

It would be nice to be able to define timestamps (start and end times, or onset and offsets) for the instances of acoustic events within an audio sample.
For that we need to create another task "define timestamps".

For the front we will take advantage of this library.
Here is an example of how to interface it with Django backend.