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!   
:warning: I think this is in Hours! (or at least that's what happens when you divide by 15).  Therefore, I think it's better to leave the above 4 lines as:
```python
return Longitude(rpol)
```
`Longitude` will make sure the value is positive and between [0,360).

Then, if someone wants the value in 'hms' could do:
```python
>>> app_ra = apparent_rightascension()
>>> print aa.to_string(unit=u.hourangle)
15h36m00s
```
On the other hand, if we want to give the value directly in `hms` then we could make the conversions ourselves first:
```python
return Longitude(rpol.to(u.hourangle))
```
I don't really have any preference of the two.. but probably the second one is better as it gives the values in the common standards.