[Feature]: An API to add custom icons to the Icon Handler list

[thakyZ]

Description

I would like to see an API to have other mods implement icons to show to on that bar where it says if robin is building or rain the next day or birthdays. Would be very nice to see.

At the moment it is just not doable to be able to add one without accessing this mod's methods via System.Reflection which is a very gross way to do it.