Store and compare worker+dataset repo versions
to implement #545


- [x] make the worker aware of its own version
- [x] store the worker version and the datasets commit hash in the cache
- [x] perform the three checks before launching (or not) the update of the cache
Store and compare worker+dataset repo versions: to implement #545


- [x] make the worker aware of its own version
- [x] store the worker version and the datasets commit hash in the cache
- [x] perform the three checks before launching (or not) the update of the cache