Added i18n

[caioflores]

I added a i18n library (react-i18next) and created the base structure to make the internationalization.
I also updated almost all the texts to the new i18n pattern and translated the file to Brazilian Portuguese.
I also added i18n as a feature of the boilerplate.

[caioflores]

@Neitsch the PR that you asked for! Tell me what you think.
There are some constants that were not translated, and I didn't created a option to change the language (we can use the browser's language).
I set up the translation options in the index.js file, I don't know if it's the best option.
All the components that needs translations will need to be exported using translate method (Ex: export default translate()(Feature);), I don't know any way that we can improve this.

[Neitsch]

Hi Caio, thank you so much for the PR! I think instead of using translate()(...) we can wrap the top level component in a i18nProvider (https://react.i18next.com/components/i18nextprovider.html) and then get { t } from this.context. I'll give that a shot tomorrow. Other than that looks really good. Thank you!