Added
* Slicing of `Tracks` ([24](https://github.com/tadejsv/EvalDeT/pull/24))
* Export of `Tracks` to CVAT for Video and a custom CSV format ([24](https://github.com/tadejsv/EvalDeT/pull/24))
Changed
* When creating tracks, if `confs` or `classes` are not provided, they are now given a default value, instead of being `None`. ([24](https://github.com/tadejsv/EvalDeT/pull/24))