Taskwarrior integration

I want checktimer to become fully integrated with [Taskwarrior](https://taskwarrior.org/). It should eventually store its data in Taskwarrior database.

- [x] (#40) add configuration file support (and store `task` and `checktimer.csv` paths there)
- [ ] (#41) add Start button to select task from the Taskwarrior database
- [ ] import currently active task from Taskwarrior at start
- [ ] store Taskwarrior task UUID in the checktimer database
- [ ] Start button should execute `task start` for the corresponding task
- [ ] Stop button / function should execute `task stop` for the currently started task
- [ ] store the duration data as a Taskwarrior [User Defined Attribute](https://taskwarrior.org/docs/udas.html) (and register the attribute automatically when needed); get rid of custom CSV file

After implementation of all those tasks, Taskwarrior installation will be required for checktimer to work.

Commencez par examiner la prise en charge de la configuration de #40 et les chemins existants de task et checktimer.csv. Suivez les actions Start et Stop ainsi que le flux de stockage actuel, puis utilisez la liste de contrôle pour vérifier la sélection et la synchronisation de Taskwarrior, le stockage de UUID et de la durée, ainsi que la suppression des données CSV personnalisées.

Rédigé par le modèle d'indexation à partir du texte de l'issue.