Transifex improvements

- Commit transifex configuration file - so that developers don't have to create it themselves
- Add a script to fetch and postprocess translations 
  - should result in smaller and clearer diffs in the future that just show the changed messages (for languages other than English; for English we need to retain the location markers, as Transifex uses them)
  - avoids importing unparseable control characters
  - avoids missing updates due to `tx pull -a` weirdness
- Full translation update