Update makemessages & transfercontext scripts to use kolibri-tools CLI

[nucleogenesis]

Summary

Description of the change(s) you made

kolibri-tools relies now on using a CLI to run the commands needed for i18n message extraction and context transfer.

This provides commands that ought to properly extract all messages for the frontend and includes an updated command for context transfer.

One thing I wondered is if we should remove the combineprofiles script as that doesn't seem to be a part of kolibri-tools/i18n any longer.

Manual verification steps performed

1. Run make i18n-upload --branch=something and see that the latest messages have been uploaded on Crowdin (or, if you're @bjester test it out on unstable 😄 )
2. Run make i18n-transfer-context and it should run, then lint, then things should be updated (assuming more context has been added on Crowdin that isn't currently in the code, anyway).

[bjester]

With additional changes (for string extraction, which I'll commit later), this has uploaded new strings to Crowdin