split up the inputs function

Seperate the existing "give me all inputs for the current model" logic
from the "give me a fieldset, with these fields in it" logic.
remove irrelevant comment
better description
Remove CellTrait from controller.

Since it isn't going to be used frequently from controllers, freeing up
the cell() method is useful and currently contentious. If we find
ourselves using cells in controllers frequently we can always re-include
the trait.

Refs #3487
Fixed bake Plugin.Classname to use Classname as the class name