Add translation engine - Google translate

[firemaples]

It's very expensive, so need to investigate how to balance the payments and incomes from ads, subscriptions, or the paid app.

https://cloud.google.com/translate/pricing

To consider

1. If this feature is added, maybe all of the users who use the Microsoft Azure translate will switch to this one if it is free to use.
2. The free quota of the Microsoft Azure translate always running out around on the 20th per month. (6,000,000 characters)
3. 20,000,000 characters will cost $10 (for the first 500,000) + $120 ($20 per million) + $60 (1/2 for buffering)
4. Test the revenue of Admob + FAN if it is more than Admob and it can cover the payment? (I think it's not) (#172)
5. Displays an ad on the result page if the user is using Google translate? (but it may be blocked by adblockers)
6. Use an embedded Google web translate service?