Update shadow.class.js

Shadow return null if null is passed.
Makes .setShadow(null) works.
Update object.js

I'm not sure, i'm sorry i tried to guess.
Update object.js

i need bigger spacebar.
or better i need to stick something on comma key that press even space after it.
Something that can bend down in one direction but not in the other, so when i press comma it push spacebar down, and when i press spacebar i don't fire a comma!
Update object.class.js

as suggested by Kienz.
Update shadow.class.js

At the end was a bad idea. If we call new fabric.Shadow() we should get a shadow whatever we pass as an argument.
Merge pull request #1427 from asturur/shadow-return-null

Update shadow.class.js - `objects.setShadow(null)` removes the sahdow
Closes #1422