Restart Token Expiration

[astojanov]

Since Translate and MicrosoftTranslatorAPI are static classes, it would be convenient if there is a method that restarts the token expiration. This becomes useful when the Bing translation is used with multiple accounts, because I don't have to wait when trying to switch to different account. Of course, it would be better if MicrosoftTranslatorAPI does not have static methods at all, so it could be used with two or more accounts simultaneously.