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!   
I do not know enough about the relationship between `Quantity` and `Angle` but I agree that a `Quantity` with angular units should work in most situations, unless there is some explicit behaviour in `Angle` that we are after.