feat(admin): class pictures for every class, and a Class Pictures tool

Adds pictures for the classes that had none (third classes, babies, mounted
classes and more), drawn from the client sprites with ROChargen in-process so
mounted classes keep their heads. Baby classes are their adult class at 2/3, like
the client draws them. The new admin tool draws missing pictures, redraws one
class, or redraws the pictures it drew (images/classes/drawn.txt), leaving the
original pictures alone. Server information skips the picture of classes without
sprites.
