Allow language to be selected within the app

[igordcard]

Allow language to be selected within the app, since some users might want to use a different language from their system's current language.
Originally requested by Luís Nabais.

[luisnabais]

Fantastic :) Thanks a lot!

If you need help in translating (which I doubt, as we are from the same country), just send me some strings.xml file and I will gladly help.

[igordcard]

Hey @luisnabais, the app is already in portuguese... but you need to choose Portuguese as the Android system language :(.

[luisnabais]

I know, maybe now the voice is better when saying the exercise names in portuguese, than was about 1-2 years ago. That's why I wanted to choose language, the English voice pronunciation was way better.