Update scripts to work with the new translation system

Now we have

- `convert_l10n.py` which takes the source code, extracts all strings, writes it into a `base.pot` file, additionally it can take inputs in the form of the internal json format and convert them to `po` files.
- `reconvert_l10n.py` which takes one or multiple `po` files and converts them to the internal json format.
- `normalize_po.py` for normalizing a `po` file to check it into a version control system.

I removed the no longer needed `update_localization.py`.