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!   
Oh... but `self.min` has already the units
```python
>>> a = 145 * u.meter
>>> a
 <Quantity 145.0 m>
>>> b = a.to(u.angstrom, equivalencies=u.spectral())
>>> b
 <Quantity 1449999999999.9998 Angstrom>
>>> print 'Wave {0!r}'.format(b)
 Wave <Quantity 1449999999999.9998 Angstrom>
```