Localised branding is incorrect

Split from the discussion in tpo/translation!148 (merged).

@ruihildt at the moment the branding for non en-US mullvad browser is wrong. Can you check in with crowdin to address the following branding issues:

1. Some translations are inconsistently using just "Mullvad" for some of the brand names (-brand-short-name, brand-shorter-name, -brand-full-name, brandShortName, brandShorterName and brandFullName), rather than a full translation of "Mullvad Browser".
2. The alpha and nightly brand files are missing the "Alpha" and "Nightly" parts of the translations.
3. The ja locale is inconsistently adding the character ー to some of the branding strings.

/cc @emmapeel