Brazilian Portuguese translation (pt-BR.js)

My humble contribution to this awesome project. :+1:  

Some notes:
- I`m not sure how to translate "upvote" and "downvote" to portuguese yet :smile:. It makes so much sense in english but it is hard to translate.
- There are some strings I couldn't translate because they are not in the i18n en.js file yet. I'll fix that on my next commit
- I'll search for typos tomorrow... I need some sleep :smile: