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!   
What units is this in? It returns a 

```python
solar_semidiameter_rad
Out[12]: <Quantity 0.00472807345206718>

solar_semidiameter_rad.unit
Out[13]: Unit(dimensionless)
```