Adding non-overlap option for time series

Hi everyone. Thanks for the amazing work with Label Studio. My team is very excited about it!

**Is your feature request related to a problem? Please describe.**

When working with **time series** for classification problems we need to avoid overlapping so that a segment have at most one label associated with it (per annotator). In our scenario, **different regions should not have overlapped positions**. On Slack @makseq told me it is not possible right now. Since our adoption of Label Studio depends on this, I'd like to make it a feature request.

**Describe the solution you'd like**

We would appreciate to have an option to block (or allow, probably as default) the overlap between different regions. If the annotator tries to label a segment which is already annotated by him / her, then it should update the associated segment to the new label.

Say I labelled segment [0, 100] as good. Then I tried to label [70, 120] as bad. The outcome we would like is:

[0, 70) -> good
[70, 120] -> bad

And not

[0, 100] -> good
[70, 120] -> bad