Minor improvements in `createDiv()`

Just as an FYI, `querySelector` can be used in a scoped manner as well ;-) 

This avoids having to add the parent ID all the time. See also [`Element.querySelector` (MDN)](https://developer.mozilla.org/en-US/docs/DOM/Element.querySelector#Browser_compatibility), it's just as compatible as `document.querySelector`.

Also moved the common `cardDiv` creation outside the `switch` statement, as this is completely type independent & a necessary action (but in general I think using a proper templating engine would make the code even cleaner, if you want I can take a look at that).