HorizonsID_type should default to None

[cbender]

Astroquery v0.4.4 onward default id_type = None to search for major bodies first. Documentation should be updated here: https://github.com/shbhuk/barycorrpy/blob/4f48f89980b5e2b3ebc8030a3c98211b24688f1b/barycorrpy/SolarSystemBC.py#L183

The desired search behavior for small bodies is passed throughout barycorrpy via the HorizonsID_type keyword. However, reflected light call to get Solar offset is still hard coded here: https://github.com/shbhuk/barycorrpy/blob/4f48f89980b5e2b3ebc8030a3c98211b24688f1b/barycorrpy/SolarSystemBC.py#L251

[shbhuk]

I'll need to double-check this. My recollection is the line 251 quoted above is getting the Solar position vector wrt the SSB, and hence the id_type = 'majorbody'