Closes#814 thanks @JortonMV !
Closes#818 thanks @egzonqj !
(both were instrumental in regards to this commit, much appreciated)
Refactors to move the slot image generation per the save file to an
extension method, instead of having 4 methods (2 in main, getQuickFiller
& getSlotFiller, and 2 in box viewer, same names).
Uses the legality marker unscaled in the bottom left corner of the
sprite.
Fielded a few ideas in IRC (a commented-out line that tinted the sprite
red remains in the src), but the folks in IRC preferred the indicator.
When toggling the legality indicator, the box viewer has to be updated
as well as the main box slots.
Move System.Drawing usage out of Core to WinForms, as System.Drawing is
not in .NET Core/Standard. Simple methods to return resource name
strings have been added instead.
