Change default FITS file fixing settings.

This should allow bad fits files to be read and fixed without raising an
exception.
first try to integrate astropy.units into sun.py
fixed the solar_semidiameter_angular_size funtion
first try to integrate utils.py
Changed tests to accept the respective quantities
used Angle, Latitude, Longitude class of astropy instead direct unit integration
changed for Latitude class
changed solar_semidiameter_angular_size to output Angle
used Angle,Longitude classes
first try to integrate time.py
used cds julian date as a return
first try to integrate unit_conversion
indentation
removed constants.au
added tests
units are getting the expected output
tests for unit_conversion, more to be added
added more tests
new tests for util
first attempt to integrate, changed MapHeader to MapCube