* Updated mailspring.appdata.xml.in and PT-BR translation
The mailspring.appdata.xml.in file is used by Flatpak to automatically build the containerized version, available in Flathub, and that file wasn't tracking Mailspring's version, showing then an older version on Flathub (main Flatpak store). Also, the Brazilian Portuguese translation is around 80% checked and corrected (also standardized a lot of different words that were the same thing, improving usability).
* Update pt-BR.json
All of the pt-BR.json was checked and verified. I've applied the necessary corrections, and tried my best to fully standardize the entire translation, because same things were being translated to different things in Portuguese.
