{{t}} supports postfixes

A `postfix` attribute for `{{t}}` helper can be used as a simple shorthand for when we want to modify translation key dynamically. It can be used for example while iterating through a list of object with some categorization property and generating a different translation key based on this property. 

I used this pattern quite a lot in my apps so maybe other guys will like it too.

Let me know if this can be improved in anyway