Adds test script

Content extracted from
https://github.com/astropy/astroquery/blob/master/astroquery/besancon/core.py
Moves besancon_api file
starting api tests
Adds original raw data
Adds tests for luminosity classes
Adds fixture to test params
Removes old test
Starting to test for new design
Adds test for luminosity

also adds test setup fixture
adds api output for SpectralType class
Tests for spectral types
Adds method to build spectral type limits
Updates api building method
Adds setting of magnitude limits
Adds ability to set colour limits
Adds test for query