add popup view

the parameter will be like ```?show_popup=[cardname]```
Thanks for the comments! I didn't know there is subformat before.

I used to have the "return" thing as it tells the reader that you don't need to read the rest which may save some time and "Exiting early allows you to pop stuff off your limited mental stack" (copy from internet to describe this :))

I will follow the current style as I don't want to have different stylistic things in the project