Added option to set expiration to 90 days

I've added an option to set the expiration date for a password to be 90 days in the future. 90 days is a common password validity for a lot of companies, due to various country laws (I'm looking at you Italy).

I've updated the localized strings files. I speak English and German, but I took a stab at Simplified Chinese and Dutch. I left French as English, since the whole file is in English.