Changed some const to #defines

Saves 6 bytes. =)
Remove stale edit / information text, update todo.txt

After editing an item (fan speed, PID values, etc) the informational
text would be left behind on the bottom of the screen. I fix this by
drawing a rectangle.

Adding this code saved 82 bytes of space, I need to know why.

Updated todo.txt with completed tasks marked off, more tasks to complete
added
Show how to exit submenus while in submenus

Most of the time the oven is just configured, profiles loaded and run,
so this serves two purposes: remind someone who hardly edits anything
how to exit a menu, and teach those new to the unit how to exit a menu.