Improve management of sensitive terms and language by the extension

[marcosmenendez]

Currently, the check done to ensure that we don't trade or store sensitive terms is done at the server instead that by the extension. This has multiple drawbacks:

1. We need more server resources
2. Depending on how this check is built, it can worsen response time and user experience
3. There might be some security risks that we could avoid if everything takes place at the extension.

Besides moving this check from the server to the extension 2 other changes have to be made:

1. Query language detection will not only look at the browser language but first of all will see if there is an hf variable in the query. If there is, this language should rule. If not, we will take the browser's
2. We should get prepared to deal with multiple languages. That means that:
   a. there should be a table of supported languages
   b. right after extension install, the extension should look at the browser language and, if supported, its table of sensitive terms should be downloaded to the extension. If it is not supported, the English table will be downloaded
   c. if the user makes a query in a different language, that first query will not be processed, but if the language is supported, the list of sensitive terms for that language is downloaded in the background at that moment
   d. this will be done up with 5 languages (or less if memory needed affects extension and browsing experience)
   e. if the user makes a query in a sixth language, the extension will download that language but first will delete the language of the query that has been made a longer time ago
   f. these dictionaries will be updated from time to time. For instance weekly. Avoiding that this update happens at the same time with all extension (random distribution)