Add Portuguese translation

Most of the translated phrases have more characters than in english. But I
verified the Subsurface user interface, and there are no strange side effects.

I had just a doubt about "trip" translation. I used portuguese word
equivalent to "expedition". Some of the diving related words we don't
translate. Even "buddy" is the word used on local diving boats!

Signed-off-by: Eduardo Ramalho <eduardo.ramalho@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>