Integration of astropy into spectra

There are many flaws in this change. Please give me your reviews, comments to make this better! 
All right, I found the units for SWAVES in [its documnetation](http://stereo-ssc.nascom.nasa.gov/ins_resources/swaves_resources.shtml)
> (c) the 2-dimensional (# of frequencies X 1440 minutes per day) array of averages in dB above the average (i.e. value-average in dB)