Tool to sync translations with Transifex

[allejok96]

This is the thing that will eventually solve #7947, #8010 and #8013

The problems

1. We don't have a tool to download translations from Transifex
2. Carla strings (among others) get uploaded to our Transifex
3. When we rename a class, the strings get a different fully qualified name, and they loose their translations
4. Translations that have been made using offline tools are never uploaded to our Transifex

How this script solves them

1. It pulls down all translations from Transifex
2. It extracts translatable strings from the files that are part of our git repo only
3. It fills up new untranslated strings with their old known translations - mimicking a paid feature of Transifex
4. It pushes both new English strings and updated translations to Transifex

When the script has been approved, it needs to be run by one of the translation maintainers to fix all the broken translations.

[allejok96]

Update: it turns out this is not needed

90% of this script is trying to solve problem 3. I've now been in touch with Transifex support and they told me their automatic translation memory fill-up feature is free for open source projects! That means the main thing this script solves needs no solving.

Problem 1 and 2 are better solved in a shell script.

Problem 4 is solved by not merging manual changes to translation files, but rather telling translators to upload their changes to Transifex so we can pulled them from there using tx pull