Automate updating translation template files

[dylanmccall]

At the moment, updating kolibri-gnome.pot with new strings is a manual process, which makes it very easy to forget. It also isn't documented. Instead, consider adding a pre-commit hook or a github workflow which updates POT and PO files automatically.

[dylanmccall]

For reference…

To update pot files, you need to have a terminal open inside the build directory generated by meson, for example using New Build Terminal in GNOME Builder. Run this command:

ninja kolibri-gnome-pot

… and this command to merge that change with all the PO files (although that might not be necessary depending on how we talk to Transifex?):

ninja kolibri-gnome-update-po