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!   
Also, how are we getting and angle of a multiplication of `cos` and `sin`? It seems we have something wrong:
On [wikipedia](http://en.wikipedia.org/wiki/Position_of_the_Sun#Equatorial_coordinates) I've got the following equation:
```python
right_ascension = np.arctan(np.cos(ob) * np.tan(true_long))
```
This needs to be checked properly (and we should properly cite the source of the equations). Ping @ehsteve.