Translate more fixed strings, make more texts configurable

[dpausp]

1. Search for strings in the code base that are not yet translated and change them to translated text.
2. Search for strings that have missing translations for specific languages and add translations.
3. Look at a messages.po file to find strings that a likely to be changed in different organizations. Replace them with a customizable_text call. The translated strings in messages.po serve as a default when there's no CustomizableText defined in the database.
4. Find all customizable_text calls, add them to missing_translations.py and add translations for them

[dpausp]

Should be customizable_text:

• tab_associated
• everything with change/counter motion
• "Go to associated"