Incorporate fetchUtils in to sdData*

The classes and methods in both sdDataRead.py and sdDataTypes.py have been updated so that they are consistent with radDataRead.py and radDataTypes.py. Specifically, sdDataPtr is more pythonic and all file fetching is now handled by fetchUtils. For more information see https://github.com/vtsuperdarn/davitpy/issues/68.

All changes that have been made are backwards compatible, ie. this code will not break exisiting code.

To test this code, simply execute `python sdDataTypes.py` in the `pydarn/sdio` directory. Further testing can include working through plotting a convection map using the following code:

    import datetime
    import matplotlib.pyplot as plt
    import pydarn.plotting.plotMapGrd
    from utils import *
    
    fig = plt.figure()
    ax = fig.add_subplot(111)

    sdate = datetime.datetime(2011,4,3,4,0)
    mObj = plotUtils.mapObj(boundinglat=50.,gridLabels=True, coords='mag')
    mapDatObj = pydarn.plotting.plotMapGrd.MapConv(sdate, mObj, ax)
    mapDatObj.overlayMapFitVel()
    mapDatObj.overlayCnvCntrs()
    mapDatObj.overlayHMB()