Rework level up dialog to behave more like vanilla

What this does exactly:
* Forbid assigning coins to maxed out attributes
* Gray out maxed out attributes (this wasn't in vanilla, but I think it's a nice touch) and don't show their multipliers
* Constant for maximum number of coins that can be assigned
* For instance, if there's only 1 attribute that is not maxed out, display just 1 coin instead of all 3
* Some code style consistency
For future reference, please only change such style issues in lines that you were already changing anyway. The potential for merge conflicts is usually not worth it.