GOES Lightcurve Fix

This PR deals with the loss of the official NOAA GOES API (issue #897) by switching to GOES data provided by

* http://umbra.nascom.nasa.gov/goes/fits/

These data go back to 1974 though I have currently implemented supported back to 1981 (the files change format). The data files are provided as FITS (as opposed to csv) and so provide healthy metadata which is provided in .meta (this deals with issue #937). Testing from 1981 to 2014 shows that this code fails only 4% of the time. The primary reason for failure is due to GOES satellites having gaps in their data. Other satellites cover those gaps but the light curve object does not currently have the capability to handle "backup" data. This PR also includes other very small improvements to lightcurve.py and time.py.