Add a feature to tell the most efficient way upgrading one's account

[yehshao0925]

Is your feature request related to a problem? Please describe.
It's not a big problem. However, I am trying to reach lv.13 recently, and I want to find a most efficient way using my gold to get xp by upgrading.

Describe the solution you'd like
I think it would be good if there is a page providing several combinition of card to upgrade one's card which may contain the most efficient way, the cheapest way or the most usable cards.