Changes to pt_BR translation

I made a more thorough check of the pt_BR translation and changed
some texts to sound more natural in the language
Removes autofocus in forms to improve accessibility

Autofocus in forms makes screen readers lose control of the tab order of
the page. So, if the page does not have one unambiguous point of
interaction (like Google's front page), the blind user gets lots.

This commit removes them.