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!   
The change above is not the same... though I maybe wrong if there are not integer quantities.  This is why:

```python
>>> print 3/float(2)
 1.5
>>> print float(3/2)
 1
```
If quantity are always `float` then there's no need to convert this to `float`.
```python
>>> print 3/2.
 1.5
```