Improve the UX for non-English speakers on Vocdoni OAuth Service

[ferranrego]

Problem:
The current implementation of login with Google on Vocdoni app involves the use of Vocdoni OAuth Service.
Google is, potentially, the main method of login for many users for Vocdoni App.
There is an important part of the Vocdoni App target audience that is not tech-savvy, and they don't have a good level of English.

Even if the texts are not complex (see image) it could be confusing for some users to see this page the first time they try to log in with their Google account for two reasons:

1. they may not fully grasp what's going on, and
2. this could be a step where users may abandon the process of creating an account, as they wouldn't find the process familiar and then they would not want to put in risk one of their most crucial online accounts.

Solution:

1. Implement multilingual support for the Vocdoni Oauth Service
2. Automatically detect the user's preferred language based on their browser (or the language selected in the app)
3. Offer the current vocdoni app languages: catalan, spanish and english.