gettor: support multilocale TB
TB 12 will not have separated installers per locale, but one per platform. In the downloads.json file they are marked as locale 'ALL'.
This commit keeps backward compatibility detecting if the locale is 'ALL' and ignoring the locale commands in the requests. Or if the downloads.json contain multiple locales gettor keeps accepting locale commands.
The locales support can be removed in the future as part of adding support for split downloads json (#42 (closed)).
Closes: #136 (closed)