Integration of astropy.units in sunpy codebase

Attempt to integrate the astropy.units into sunpy. Every function that were taking or giving a quantity now must have astropy quantity associated with them. Please tell me if I have made mistakes anywhere, or if it could be done in better way, I will make changes! 
Thank you!   
Where did you get the units are `W/m**2`? Callisto does not have real units. We could use `u.count` but that would not be right either... as they are not counts.  Maybe there's a better unit to use..