Add Brazilian Portuguese translation and reorder LINGUAS in alphabetical order

[Tuba2]

This PR includes the following changes:

1. Addition of a pt_BR.po file to the /po directory, containing a Brazilian Portuguese translation for the app, based on the latest PO file available in the repo;
2. Edit to the LINGUAS file to include a "pt_BR" line, in order to make the Brazilian Portuguese translation available to the app;
3. Reordering of the lines in the LINGUAS file in order to keep the language identifiers in alphabetical order.

Hope my work can be of use and help the app get more Brazilian Portuguese-speaking users. Thanks for the app!

[Tuba2]

I should also add 2 things:

1. I've considered @Luiz-C-Lima 's translation from Add Brazilian Portuguese Translation #118 when creating mine. I believe I've made it more consistent all around and also more accessible to Brazilian Portuguese-speakers with no knowledge of English. He can check my version and see if he agrees with my choices.
2. The LINGUAS file does not include a "nl" line, even though the Dutch translation is already in the /po directory.

[Luiz-C-Lima]

I ask the maintainer to not accept either pull request yet, I believe that both translations have their own strengths, I will create a new translation with the better parts of both translations and send a pull request to @Tuba2 's repository with the updated translation and the reasoning of those changes.